Calcium and Magnesium Removal

Calcium and magnesium are two elements that are often found in water, especially in hard water. These elements can cause various problems, such as scaling in pipes and appliances, difficulty in forming a lather with soap, and issues in industrial processes. Therefore, removing or reducing the concentration of calcium and magnesium from water is often necessary. Here are some common methods used to remove calcium and magnesium:

1. Ion Exchange (Water Softening)

  • Process: Calcium and magnesium ions in the water are exchanged with sodium or potassium ions.
  • Application: Widely used in residential and industrial settings.
  • Equipment: Water softeners that contain a resin bed.
  • Note: The sodium or potassium ions do not cause hardness, thus "softening" the water.

2. Reverse Osmosis (RO)

  • Process: Water is forced through a semi-permeable membrane that removes ions, molecules, and larger particles.
  • Application: Used in both residential and industrial settings, and for desalination of seawater.
  • Equipment: RO systems that include a high-pressure pump and membrane.
  • Note: RO can remove not only calcium and magnesium but also other contaminants.

3. Lime Softening

  • Process: Adding lime (calcium hydroxide) to water to precipitate calcium and magnesium as their hydroxides.
  • Application: Commonly used in municipal water treatment plants.
  • Equipment: Tanks for lime mixing and sedimentation basins.
  • Note: This method also helps to stabilize the pH of the water.

4. Chelation

  • Process: Chelating agents bind with calcium and magnesium ions, preventing them from causing hardness.
  • Application: Often used in detergents and industrial processes.
  • Note: Chelating agents like EDTA can sequester calcium and magnesium ions.

5. Electrodialysis

  • Process: Electric current is used to drive ions through selective membranes, separating them from the water.
  • Application: Used in some industrial processes and water desalination.
  • Equipment: Electrodialysis unit with anion and cation exchange membranes.
  • Note: Effective in removing various ions from water.

6. Distillation

  • Process: Water is boiled, and the steam is condensed to obtain purified water.
  • Application: Can be used in laboratories and some industrial processes.
  • Equipment: Distillation apparatus.
  • Note: Energy-intensive and not typically used for large-scale water treatment.

7. Sequestering

  • Process: Chemicals are added to water to form soluble complexes with calcium and magnesium, keeping them in solution.
  • Application: Used to control scale formation in pipes.
  • Note: Does not remove calcium and magnesium but prevents them from precipitating.

8. Nanofiltration

  • Process: Similar to RO but uses membranes with larger pore sizes.
  • Application: Suitable for partial softening and some industrial processes.
  • Equipment: Nanofiltration system.
  • Note: Allows some monovalent ions to pass through while rejecting divalent ions.

Each method has its own advantages and disadvantages, and the choice of method will depend on the specific requirements of the application, such as the desired water quality, available budget, and scale of operation.

Calcium and Magnesium Removal

Calcium Removal

Calcium is one of the most abundant elements in water. Calcium levels in your water are not harmful to the human body, but cause a variety of issues related to water quality. If you feel that there might be an abundance of calcium present in your water, consider the symptoms below and review the best treatment options to fit your needs.

Symptoms of Calcium in Water

Calcium in water leaves the distinct tell-tale sign of crusty white scaling, or calcification, on your water fixtures and dishes. High levels of calcium can cause calcification which blocks faucets and causes low water pressure. In addition, another sign of calcium in your water is the lack of suds from soaps and shampoos. If your appliances , such as your dishwater or hot water heater are wearing out quickly, this could be the cause of high levels of calcium. A build up sediment on your hot water heater may be lowering your efficiency, which in turn means higher utility bills. In fact, hard water expenses could raise your utility bills by over $800 per year.

Treatment Options for Calcium in Water

If you’re looking for the best calcium water filter, then you’re in the right place!

Water contains many minerals from the earth, including calcium and magnesium, which makes the water hard, leading to limescale formation on tap and other instruments.

Among these minerals, calcium is an important element.

Though calcium is important for drinking water, the availability of calcium causes the white shot or films in your dishes and shower.

Calcium and magnesium contaminated water leads to hardness in water, which can damage your hair, skin, nails, and clothes during laundry.

So, calcium becomes a problem for daily chores, and so it becomes necessary to remove calcium and magnesium by using water softeners.

Calcium and magnesium are minerals (ions) found in hard water. Water softeners are used to remove those minerals from the hard water. Here’s how.

Water softeners contain two separate chambers: a brine tank and a resin tank. The resin tank is where the water softening takes place.

Water softeners make use of a process called ion exchange to remove hardness ions from the water. The water softener resin tank contains a bed of small beads that have sodium ions electrostatically attached to them. The water softener pumps hard water through this resin bed and the hardness ions are exchanged with the sodium ions. That is, the hardness ions will stick to the resin and displace the sodium ions which then end up in the softened water.

Ion exchangeOver time the resin fills up with hardness ions and can no longer soften the water. At that point the water softener must regenerate. Salt brine from the brine tank is pumped into the resin and that salt brine washes away the hardness ions and replaces them with a fresh layer of sodium ions. The softener resumes softening more water.

The influence of calcium and magnesium in drinking water and diet on cardiovascular risk factors in individuals living in hard and soft water areas with differences in cardiovascular mortality


The role of water hardness as a risk factor for cardiovascular disease has been widely investigated and evaluated as regards regional differences in cardiovascular disease. This study was performed to evaluate the relation between calcium and magnesium in drinking water and diet and risk factors for cardiovascular disease in individuals living in hard and soft water areas with considerable differences in cardiovascular mortality.


A random sample of 207 individuals living in two municipalities characterised by differences in cardiovascular mortality and water hardness was invited for an examination including a questionnaire about health, social and living conditions and diet. Intake of magnesium and calcium was calculated from the diet questionnaire with special consideration to the use of local water. Household water samples were delivered by each individual and were analysed for magnesium and calcium.


In the total sample, there were positive correlations between the calcium content in household water and systolic blood pressure (SBP) and negative correlations with s-cholesterol and s-LDL-cholesterol. No correlation was seen with magnesium content in household water to any of the risk factors.

Calcium content in diet showed no correlation to cardiovascular risk factors. Magnesium in diet was positively correlated to diastolic blood pressure (DBP). In regression analyses controlled for age and sex 18.5% of the variation in SBP was explained by the variation in BMI, HbA1c and calcium content in water. Some 27.9% of the variation in s-cholesterol could be explained by the variation in s-triglycerides (TG), and calcium content in water.


This study of individuals living in soft and hard water areas showed significant correlations between the content of calcium in water and major cardiovascular risk factors. This was not found for magnesium in water or calcium or magnesium in diet. Regression analyses indicated that calcium content in water could be a factor in the complexity of relationships and importance of cardiovascular risk factors. From these results it is not possible to conclude any definite causal relation and further research is needed.

between the western areas with high mortality and soft water and the eastern areas with low mortality and hard water. The hardness of water defined as the sum of the content of calcium and magnesium, was shown to be of considerable influence on the differences in mortality compared to major risk factors .

The incidence of coronary heart disease varies widely in different geographical regions over the world and serious epidemiological studies have been carried out to identify variables that could explain this fact. The role of water hardness has been widely investigated and evaluated for many years in several studies where regional differences in cardiovascular disease have been discussed .

Extensive reviews indicate the difficulties in interpreting the results of many studies and also point out the need for further studies including intervention. Previous studies have found positive correlations between water and dietary magnesium and calcium and blood pressure . In Finland and South Africa it was found that the incidence of death ascribed to ischaemic heart disease is inversely correlated with the concentration of magnesium in drinking water. A post mortem study has demonstrated significantly reduced intramyocardial and coronary arterial wall magnesium levels in road accident victims who lived in areas where water supplies have low magnesium content . However, other studies could not confirm these findings. In a Swedish study the skeletal muscle magnesium levels were significantly higher in persons living in an area with higher water magnesium. The concentration of magnesium in striated muscle has been used as a marker to evaluate the ion content in the soft tissue and therefore we conducted muscle biopsy in a sub-group of individuals.

Mineral-rich water could provide an important supplementary contribution to total calcium and magnesium intake according to results from a French study.

In a Swedish case control study magnesium and calcium in drinking water were associated with lower mortality from acute myocardial infarction in women but not with the total incidence. In these studies there was no recording of the diet. The presence of risk factors was ascertained by interviews of surviving cases and controls, and no analyses of lipids were made.

There are however also studies where the results are not as conclusive, in a case control study of men in Finland with a 10-year follow-up there were no significant differences in concentrations of serum calcium and serum magnesium between cases who died from cardiovascular diseases and controls. In a study of magnesium in drinking water supplies and mortality from acute myocardial infarction in north-west England, there was likewise evidence of an association between magnesium and cardiovascular mortality. The aim of the present study of individuals living in two of the 76 municipalities on the extreme in our previous study was to show the influence of magnesium and calcium intake in water and diet on major cardiovascular risk factors; s-cholesterol, s-TG, s-LDL, SBP and DBP.

The water from the major water supplies in the municipality in the east had a higher degree of hardness, 66 mg/ml of calcium and 4.1 mg/ml of magnesium, than in the municipality in the west with 8.8 mg/ml and 0.74 mg/ml respectively. Age-standardised rates for total mortality, mortality from cardiovascular disease and ischaemic heart disease (IHD) for men and women aged 45–64 years in the two municipalities 1989–98 are shown in Table. All differences were significant p < 0.0001 with higher mortality rates in the western municipality.

Table 1 Standardised mortality cases per 1000 inhabitants, population and risk ratio (SMR) for inhabitants aged 45–64 in the two municipalities in the west and east part of Sweden 1989–1998.


Two random samples of 120 individuals aged 40–59 years were drawn from the official register of the total population in each of two municipalities. One of the municipalities, Tocksfors, in the western part of Sweden, was characterised by soft water and high cardiovascular mortality, and the other, Osthammar, situated in the eastern part of Sweden, by hard water and low mortality. Both municipalities are mainly rural areas with a population of the same size.

Inclusion criteria were being resident in the municipality for at least 5 years and also being supplied by the same water source for at least 5 years. Exclusion criteria were clinical conditions known to influence the metabolism of magnesium, such as acute myocardial infarction during the last 6 months, resection of the intestine, kidney failure, thyroid dysfunction with pharmacology treatment, use of diuretics, failure of the liver or abuse of alcohol.

In total, 105 men and women in Tocksfors and 102 in Osthammar matched the inclusion and exclusion criteria and participated in the study.

The individuals were invited to the local primary care centre for a physical examination. Each person delivered a tap water sample from his or her household on the day of the visit to the primary care centre.

Height and weight were measured in centimetres and kilograms and body mass index, (BMI) kg/m2 was calculated. Blood pressure was measured in recumbent position after 5 minutes rest. Urine was collected during 24 hours in bottles prepared and delivered by the laboratory. The individuals were instructed and informed about the sampling by the nurse.

Blood samples were taken and a questionnaire was filled out by the participants and monitored by the study nurse. The questionnaire contained questions about social situation, medical history of cardiovascular disease, liver or kidney disorder, thyroid dysfunction and diabetes. Smoking and alcohol habits were also recorded.

Muscle biopsy in striated muscle (m. vastus) was conducted in 67 subjects, 29 in the western and 38 in the eastern municipality. Each individual in the study was asked to give his or her consent for the biopsy and all in this sample agreed.

Assessment of the dietary intake was made by a food frequency questionnaire based on an earlier questionnaire developed at the Department of Environmental Medicine, Göteborgs University.

The questionnaire was specifically aimed at quantitatively assessing magnesium and calcium in the diet, regarding portion sizes and use of local tap water in drinks and in food preparation. The use of mineral salt (Seltin) was also assessed.

There were twenty-two questions about the consumption of milk and milk products, fish, meat, bread and cereals, fruit, vegetables, nuts and snacks and four questions on the use of beer, wine, mineral water and tap water based drinks (coffee, tea, fruit juice etc).

The Department of Clinical Nutrition evaluated of the individual intake of magnesium and calcium. Individual basal metabolic rate (BMR) was calculated according to Schoefield et al. based on sex, age, weight and height. In this population, the daily total energy expenditure was estimated to be 1.5* BMR. This figure was used as an indication of the portion size (small, normal or large) for main meals in the individual calculations. For other types of food, household measures such as bottle, spoon, cup, slices etc., and standard portion size according to Swedish standards were used .

Data for calcium and magnesium content in foods were taken from food tables in "Swedish Food Data base" from the National Food Administration, and from manufacturers analyses of mineral water and from actual tap water analyses. For food ingredients such as rice, rolled oats, legumes (peas, beans, lentils) and, pasta, the calculations were made on dry weight, adding an appropriate amount of tap water or milk, for the preparation. The estimation of dietary calcium and magnesium, derived from local tap water was based on water analyses and the individual amount of water used, including food preparation and drinks.

Laboratory methods

Blood was drawn after an overnight fast, with no alcohol the last 24 hours and no smoking the last 3 hours, by venipuncture and in Vacutainer Tubes. Analyses were made at the Laboratory of Clinical Chemistry, Central Hospital in Karlstad. Calcium and magnesium content in whole blood, serum, muscle and urine was determined by atomic absorption spectrophotometry. Glycosylated haemoglobin, HbA1c, was determined by the ion exchange HPLC method. Water samples were taken in supplied bottles from the laboratory on the morning of the visit to the health centre and analysed for magnesium and calcium. The results were given in mg/l.


The statistical package SPSS 10.1 was used for statistical analyses.

Differences between groups regarding continuous variables were analysed using Student's T-test and, for variables judged as skewed, the Mann-Whitney U-test. Regarding categorical variables the chi-squared test was used. Correlations were calculated using Spearman's rank-correlation coefficient.

Multivariate linear regression was performed to evaluate the relative importance of factors possibly contributing to the variation in risk factor levels. A stepwise procedure was used, whereby factors not significantly contributing were excluded. Residuals were checked for normality and showed no disturbing features.

Internal dropout rate did not exceed 1% for any of the items.

P-values less than .05 were regarded as significant


Table shows descriptive socio-economic data. Age and gender were similar in the groups. The individual educational level was higher in the eastern municipality. The individuals in the west had been residents in the municipality more years than in the east.

Table 2 Descriptive socio-economic data.

Table shows health variables of the participants. The prevalence of previous cardiovascular disorders, hypertension, BMI and diabetes did not differ between the groups, nor did the use of medication. Systolic blood pressure was higher, and smoking more common in the east than in the west.

Table 3 Health variables.

Laboratory variables are presented in table The mean s-cholesterol was significantly higher in the west, as was the level of s-LDL-cholesterol and LDL/HDL. Water supplied by the municipality was used by 24.5% in the eastern municipality and 61.5% in the western, the rest using private wells.

Table 4 Laboratory variables.

The total hardness of water, defined as the sum of calcium and magnesium, in household water in the two municipalities is presented in Figure.

Figure 1

Water hardness, defined as the sum of calcium and magnesium (mg/l), in household water delivered by the study participants in the western and eastern municipality.

The median content of calcium in the household water was 12.5 mg/l in the west and 58 in the east with minimum and maximum values of 4.5–76.0 and 0.5–128.0 respectively. The median content of magnesium in the household water was 3.3 mg/l in the west and 5.4 in the east with minimum and maximum values of 0.7–14.3 and 0.1–13.5 respectively. The water from the major water supplies in the municipality in the east had a higher degree of hardness but the ratio Mg/Ca being similar in the two areas, 0.06 in the east and 0.08 in the west. In the household water however, the Mg/ Ca ratio was 0.18 in the west and 0.09 in the east, which is statistically significant p = .0001.

The use of water filter was 3.8% in the west and 10.8% in the east.

Of the individuals using water in the lowest quartile of water hardness were 92.3% living in the western municipality and 96.1% using water in the highest quartile were living in the eastern municipality. Dietary intake variables for the individuals in the two municipalities are presented in table and

Table 5 Dietary intake of calcium, mg/day, median (min-max).
Table 6 Dietary intake of magnesium, mg/day, median (min-max).

The median intake of calcium from diet did not differ significantly between groups living in the eastern and western municipalities. There were however, great inter-individual differences. Overall, household water accounted for small amounts of the daily calcium and magnesium intake in both municipalities.

Milk and cheese were the main sources of calcium in the diet (around 60%). In both areas the most important sources of calcium besides milk products were bread and cereals (6–7%), followed by chocolate (5%) and vegetables and fruit in the western area and by local water (4%) and vegetables (3%) in the east.

Magnesium intake from diet was higher in the west (p = 0.028). Important sources for magnesium were bread and cereals as well as milk products, each contributing about 25% of the magnesium intake in both areas. Potatoes (6–7%), meat and fish (5–7%), vegetables, fruit and berries (5%) also supplied small amounts of magnesium. Overall, the participants in the western areas tended to consume more milk and chocolate and less beer/ wine than in the eastern areas.

In Table 7 correlations between calcium and magnesium in water and cardiovascular risk factors are presented in the total study population and for men and women. There were positive correlations between calcium in water and systolic blood pressure (SBP), and negative correlation for s-cholesterol and s-LDL-cholesterol. These correlations were also found for women, while for men only a correlation to SBP was found.

Table 7 Correlations between Ca and Mg in water and cardiovascular risk factors, calcium in serum and urine, and magnesium in serum, muscle and urine. Total study population and men and women. Spearman's rank correlation coefficient.

The same results were found for total water hardness defined as the sum of calcium and magnesium.

There were no correlations between the ratio urine calcium/urine magnesium and SBP or DBP.

No correlations were found between magnesium in water and cardiovascular risk factors in the total population, although, for women there was a positive correlation to s-calcium and a negative one to magnesium in muscle. For men there was a positive correlation to magnesium in muscle.

No significant correlations between calcium in diet and the risk factors were found. For magnesium in diet there was a positive correlation to DBP.

Correlations between content of calcium and magnesium in serum, urine and muscle with cardiovascular risk factors are shown in table For s-calcium there were positive correlations to s-cholesterol, s-triglycerides, s-LDL, SBP, DBP, and HbA1c. For s-magnesium there were positive correlations to s-TG and DBP and a negative correlation to s-HDL.

Table 8 Correlations between calcium and magnesium in serum, muscle and urine and major cardiovascular risk factors. Spearman's rank correlation coefficient.

In regression analyses controlling for age and sex 18.5% of the variation in SBP was explained by the variation in BMI, HbA1c and calcium content in water. Some 27.9% of the variation in s-cholesterol could be explained by the variation in s-TG, and calcium content in water.


In this study we used individual data to evaluate the role of water and diet magnesium and calcium on major cardiovascular risk factors, s-cholesterol, s-TG, s-LDL, and SBP and DBP. Since water compositions vary substantially even within small geographic areas using data from municipality water supplies could give an incorrect risk estimate. We therefore used the composition of water from the actual use of household water. We found, however, that even if 92.3% and 96.1% respectively of the individuals living in soft and hard water areas were using household water in the lowest and highest quartile of water hardness there were great variations within the geographic area.

Since magnesium has been considered the water factor most likely to have an influence on cardiovascular mortality attention in the study was focused on magnesium as well as water hardness and calcium.

We have used the available methods for analysing magnesium and calcium; in serum, whole blood, and urine. Since there is only a weak correlation between the magnesium content of different body compartments, it remains unclear which method best reflects body magnesium. This fact makes it hard to evaluate the role of s-magnesium as the marker of magnesium status of the body.

The content of magnesium in drinking water in various countries was found to range between 0 and 111 mg/l according to previous studies. The magnesium content in the water of Sweden is lower than in most other countries due to geological circumstances. This could explain why magnesium in our study is not shown to be the water factor.

The mean daily intake of calcium, 1023 mg to 961 mg in the west and east respectively, was close to the average dietary calcium supply in Sweden of 1100 mg (1995–1999) . Unfortunately, there are no statistical data from Sweden regarding magnesium supply, the recommended daily intake being 350 mg for men and 280 mg for women. The average daily intake in the UK is 323 mg for men and 237 mg for women . In our present study the daily intake were 250 mg in the west and 221 mg in the east. There were large variations within the groups as regards the consumption of various foods, and consequently also large variations in the intake of minerals. Milk consumption varied from nothing to more than 2 litres a day; most persons not drinking milk had a high intake of cheese, but – in fact about 50% of both men and women got less calcium and magnesium than recommended .

The negative correlations we found between calcium in water and s-cholesterol and s-LDL indicated that a high content of calcium could lower the levels of s-cholesterol and s-LDL but on the other hand increase SBP. The individuals living in the east had higher SBP. The absence of correlations between calcium and magnesium in water to calcium and magnesium in serum should be noted. The lack of correlation between magnesium content in water and risk factors is unclear and needs further research.

There was a significant correlation between s-magnesium and s-calcium, which is an expected normal condition in healthy subjects.

S-calcium showed several positive correlations to cardiovascular risk factors: s-cholesterol, s-TG, s-LDL, SBP, DBP, and HbA1c and s-magnesium had positive correlations to s-TG and DBP, and a negative correlation to s-HDL. This indicates that high s-calcium and s-magnesium increases the levels of metabolic factors that are considered to elevate the risk for cardiovascular disease.

The regression analyses of the variation in s-cholesterol, and SBP demonstrate the complexity of interactions between major risk factors where calcium in water could be a factor of importance.

Since a major part of the magnesium and calcium intake is known to be dietary, this study included diet recordings on an individual basis. The food frequency questionnaire used was designed to capture the calcium and magnesium in the diet.

When considering hard water as a protective factor for cardiovascular disease, the importance of locally produced food has also been discussed. A study has been performed to evaluate the changes in the mineral composition of food as a result of cooking in hard and soft water . The results show that magnesium is extracted from food by cooking, most pronounced in soft water. The calcium content increased in food when cooked in hard water and decreased in soft water. In the present study, the mineral content in foods like pasta and beans was supposed to have increased, e.g. 50 g of pasta plus 100 g of water corresponds to 150 g of cooked pasta including the minerals in local water. Otherwise, most of the local water was consumed as drinks.


This study of individuals living in soft and hard water areas showed significant correlations between the content of calcium in water and major cardiovascular risk factors. This was not found for magnesium in water or calcium or magnesium in diet. Regression analyses indicated that calcium content in water could be a factor in the complexity of relationships and importance of cardiovascular risk factors. From these results it is not possible to conclude any definite causal relation and further research is needed.

Calcium and Water Hardness


Calcium, Ca2+

Calcium, in the form of the Ca2+ ion, is one of the major inorganic cations, or positive ions, in saltwater and freshwater. It can originate from the dissociation of salts, such as calcium chloride or calcium sulfate, in water.

\text_\text{(s)} \to \text^\text{(aq)} + 2 \text^{-}\text{(aq)}\text_\text{(s)} \to \text^\text{(aq)} + \text_\text{}^\text{(aq)}

Most calcium in surface water comes from streams flowing over limestone, CaCO3, gypsum, CaSO4•2H2O, and other calcium-containing rocks and minerals. Groundwater and underground aquifers leach even higher concentrations of calcium ions from rocks and soil. Calcium carbonate is relatively insoluble in water, but dissolves more readily in water containing significant levels of dissolved carbon dioxide.

The concentration of calcium ions (Ca2+) in freshwater is found in a range of 0 to 100 mg/L, and usually has the highest concentration of any freshwater cation. A level of 50 mg/L is recommended as the upper limit for drinking water. High levels are not considered a health concern; however, levels above 50 mg/L can be problematic due to formation of excess calcium carbonate deposits in plumbing or in decreased cleansing action of soaps. If the calcium-ion concentration in freshwater drops below 5 mg/L, it can support only sparse plant and animal life, a condition known as oligotrophic. Typical seawater contains Ca2+ levels of about 400 mg/L.

Calcium Hardness as CaCO3

When water passes through or over mineral deposits such as limestone, the levels of Ca2+, Mg2+, and HCO3 ions present in the water greatly increase and cause the water to be classified as hard water. This term results from the fact that calcium or magnesium ions in water combine with soap molecules, forming a sticky scum that interferes with soap action and makes it “hard” to get suds. One of the most obvious signs of water hardness is a layer of white film left on the surface of showers. Since most hard-water ions originate from calcium carbonate, levels of water hardness are often referred to in terms of hardness as CaCO3. For example, if a water sample is found to have a Ca2+ concentration of 30mg/L, then its calcium hardness as CaCO3 can be calculated using the formula

(30 mg/L Ca2+) × (100 g CaCO3 / 40 g Ca2+) = 75 mg/L calcium hardness as CaCO3

Note that 30 mg/L Ca2+ and 75 mg/L calcium hardness as CaCO3 are equivalent—they are simply two different ways of expressing calcium levels. The value of calcium hardness as CaCO3 can always be obtained by multiplying the Ca2+ concentration by a factor of 100/40, or 2.5.

Another common measurement of water hardness is known as total hardness as CaCO3. This measurement takes into account both Ca2+ and Mg2+ ions. On average, magnesium hardness represents about 1/3 of total hardness and calcium hardness about 2/3. If you are comparing your own test results of calcium hardness as CaCO3 with results in publications that use units of total hardness as CaCO3, you can estimate total hardness by multiplying the calcium hardness by 1.5. See Test 14, Total Water Hardness, for further information about this topic.


  • Measure the calcium ion concentration in a stream or lake, in mg/L as Ca2+, using a Calcium Ion-Selective Electrode (ISE).
  • Determine the calcium hardness as CaCO3 in mg/L.

Water Softening

Hard water causes gray or white deposits when water is heated. Water softening can be used to reduce these symptoms.

A typical salt-based water softener.

For example, "hard water is what causes the white scale buildup on my pots," or "soft water doesn't leave a detergent film on my fresh-washed clothes or fixtures." Some might even contend that soft water makes their skin smoother and hair more silky and manageable. While these observations may be true, they may not be substantial reasons to purchase a water softening device. It is also important to note that water softeners will not necessarily remove any of the more serious drinking water contamination problems. An understanding of the chemistry of hard and soft water and the treatment process used to produce softer water can help you answer the question, "Do I need to soften my water?"

Hard Water/Soft Water

Whether a water supply is labelled "soft" or "hard" is dependent on the presence of two highly soluble minerals, calcium and magnesium. From a health standpoint, these minerals have no adverse effects and are, in fact, essential daily nutrients. It is minerals that give water the refreshing flavor many people find desirable. However, when calcium and magnesium permeate water, they buildup on contact surfaces, possibly plug pipes and damage water heaters, and decrease the effectiveness of soaps and detergents. At this point the water is said to be hard.

Water hardness is expressed in one of two units of measurement. The first unit is parts per million (ppm) of calcium carbonate, a term equivalent to the concentration of dissolved calcium and magnesium. Using this equivalent simplifies hardness calculations. One ppm means that one unit of calcium carbonate is dissolved in one million units of water. Parts per million is also equal to milligrams/liter (mg/l). A second expression of hardness is grains per gallon (gpg) of calcium carbonate. A gpg is used exclusively as a hardness unit and equals approximately 17 mg/l or ppm.

If you have your water tested, the report will use one or both of these units to tell you how hard your water is. Since the level of calcium carbonate means little to water consumers, water specialists have classified levels of hardness. Table 1 shows these classifications.

Table 1. Water Hardness Classification.
Classification Grains per gallon
Parts per million or
milligrams per
liter (ppm) or mg/l)
Soft Less than 1.0 Less than 17
Slightly hard 1.0 to 3.5 17 to 60
Moderately hard 3.5 to 7.0 60 to 120
Hard 7.0 to 10.5 120 to 180
Very hard Greater than 10.5 Greater than 180

The Water Softening Process

Once water hardness is known, you have two options. You can live with the hardness level, recognizing that levels below 7.0 gpg will probably not cause major scaling and soap film, or treat the water to reduce the calcium and magnesium present. A water softener, also called an ion exchange unit, will effectively accomplish the latter option.

Ion Exchange

Because water softening devices have long been available in the water treatment industry, the technology is highly developed and in most cases works well to reduce the hardness level.

How does ion exchange work? A physical and chemical process filters the water through an exchange media known as resin or zeolite. Typically, the resin is a synthetic or natural, sand-like material coated with positively charged sodium ions. As the calcium and magnesium dissolves into positively charged ions, an ion exchange environment is created. The water flows through the unit while the resin releases its sodium ions and readily trades them for the calcium and magnesium ions. The water flowing out of the device is now considered soft.


Clearly the resin is not an inexhaustible exchange site. When all the sodium exchange sites are replaced with hardness minerals, the resin is spent and will no longer soften water. At this point, the water softener will need to be run on an alternate cycle called regeneration. During this cycle, resin is backwashed with a salt solution. The brine is reverse flushed through the system taking with it the calcium and magnesium ions that had been adsorbed on the resin. Once backwashing is complete, the softener can be returned to use. Some water softeners will automatically switch to the operation cycle. Others have a manual switch. Figure 1 illustrates both cycles of the water softening process--ion exchange and regeneration.

Figure 1. A typical water softener showing ion exchange and regeneration.

Kinds of softeners

Although many brands and models of ion exchange units exist on the market, all essentially perform the same with minor differences in extra features, flow rates, etc.

Nearly all softeners fall into one of two categories. Timed models have programmable timeclocks that will regenerate on a predetermined schedule and then return to service. These work well for households that are on regular water-using cycles but will waste more water and salt because they regenerate whether the resin needs it or not. Demand-control models, with either electrical and mechanical sensors, usually regenerate after so many gallons of water have been softened. Such models are convenient if you have a fluctuating water use schedule.


No matter which model you choose, all water softeners need to be properly maintained. The brine solution must be mixed and stored in the brine tank. Periodic clogging of the resin also requires special attention. For example, if the raw water supply is turbid it may clog the resin with mud and clay. Sometimes, normal backwashing with water will solve this problem. If not, slowly stir the resin during the backwash cycle to help break up the material. Likewise, bacteria and fungi also form mats in the resin that reduce its effectiveness. Disinfecting the water prior to softening or periodically cleaning the softener with chlorine bleach will eliminate these nuisances. However, read the manufacturer's instructions before adding any chemicals to the unit.

Iron fouling is another common maintenance problem for water softeners. Although colorless, reduced iron will be removed by the unit, red-oxidized iron (iron that has been exposed to air or chlorine) will clog the resin. Filtration prior to softening insures that oxidized iron is not processed in the softener. If the resin has already been fouled, commercial cleaners are available. Again, it is advisable to check the manufacturer's instructions for special precautions.

In some instances, resins can not be washed of contaminants and will need to be replaced. (This should not be the case if the resin is periodically regenerated and maintained.) Consult your water softener dealer for information on resin replacement.


Water softening costs depend on factors such as installation, maintenance fees, and size of the unit. You can also expect that with more convenience features, the price of the unit will increase. An average range for the hardware only is around $500-$1500.

Advantages and Disadvantages of Water Softening

As the water treatment industry has grown in the U.S., the concept of water softening has often been misconstrued as a purifying, cleansing or conditioning process. This is due largely to exaggerated advertising and, in part, to consumer misconceptions about water treatment. But the reality is that water softening simply removes hardness minerals and eliminates problems that are a nuisance and not a threat to human health. The decision "to soften or not to soften" is a matter of personal preference not necessity. However, water softening does have advantages, and disadvantages, that make this decision a significant one.


Most consumers would agree that hard water leaves scales on pots, soap films on skin, and detergent curds in the washing machine. More importantly, scales can also buildup on hot water heaters and decrease their useful life. Soap film and detergent curds in bathtubs and appliances indicate that you are not getting the maximum cleaning action from these products. Soft water not only eliminates these nuisances but also protects appliances and saves cleaning time.

There are other advantages to water softening, as well. It is a well developed technology that has been used in homes for almost 65 years. The equipment is reliable, effective, and widely available, providing consumers with convenient features and a selective market. The simple technology of softening makes it easy to bypass toilets and outdoor faucets. Finally softening systems are adaptable for mixing softened and unsoftened water to produce a lower hardness level.


The major disadvantage to water softening is the potential health risks for people on low sodium diets. The exchange of hardness minerals for sodium adds 7.5 milligrams per quart for each gpg of hardness removed. In addition, calcium and magnesium are eliminated from the homeowner's diet.

Maintenance is another consideration. While you can purchase models with special features that do everything but add the salt, you will pay for each additional feature. The tradeoff will be cost for convenience and you have no long-term guarantee that the special feature will not fail. Depending on the water source, you may have to filter turbid water or disinfect bacteria-laden water--all before it even reaches the softening unit. Finally, if you own a septic system, you should consider the additional load on your drainage field from backwashing and regeneration. Estimates indicate that about 50 gallons of water are used for each regeneration cycle. This may or may not cause hydraulic overload of the septic system.

Selecting a Water Softener

If after weighing the advantages and disadvantages of water softening, you decide to soften your water, the next question you must consider is "How much?" Have the water tested by an independent lab and determine its classification from Table 1. Although many water softening companies offer free hardness testing, its best to have a third party evaluation. An independent lab test is not expensive and will protect you from being oversold.

Next, recognize that unless your water is extremely hard, all the incoming water does not need to be softened. Showers, sinks, and laundry hookups probably should be softened; toilets, outside spigots, and basement sinks can be bypassed. In some cases, you may desire to soften the hot water only. Measure the water usage at the designated hookups for each person in the household or use the following table as a guide.

Table 2. Guidelines for estimating water use.
Use Water Usage
Household drinking and cooking 1 gal/person/day
Bathing and showering 25-60 gal/use
Dishwashing 6-19 gal/use
Clothes washing 20-33 gal/use

You can estimate the size of the softener you will need and the regeneration cycles using the following calculation as an example:

Sample calculation for determining a regeneration cycle.

20,000 = Sample capacity (number of grains per regeneration)
75 gallons = average person usage per day
10 gpg = raw water hardness
4 people = household size

75 gallons (10 gpg) x 4 = 3,000 grains per day used
20,000/3,000 = about 6-7 day regeneration

Finally, using this information, select a softener that meets your needs and provides the conveniences you desire. Recognize that all softeners use essentially the same process. For this reason, most softeners are not rated for effectiveness, only for convenience features like handiness, size, maintenance requirements, safety and cost. These features are a matter of personal preference. So be wary of sales people who attempt to sell you on their product's ability to outlast or "outsoften" other products. Most water softeners are hardware on which you can rely.

Prepared by Paul D. Robillard, Associate Professor, Agricultural Engineering, William E. Sharpe, Professor, Forest Hydrology, and Bryan R. Swistock, Extension Associate.


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