What 'Detected', 'Median', and 'Range' Mean in the Sampling Record on This Page
The U.S. Geological Survey conducted groundwater sampling in the aquifer 112DFSF within FIPS 180, CT, analyzing 69 samples from 19 wells between 2015 and 2025. Every sample detected calcium and magnesium minerals linked to mineral spotting on dishes. The median value, which represents the middle value in the recorded data, was 66.2 mg/L. This means half the samples measured mineral concentrations above this level and half below. The range varied widely, from 15.9 to 1680.0 mg/L, reflecting natural variations in the area’s groundwater. None of these results exceeded any federal health-based thresholds, affirming these minerals’ presence but not signaling unsafe water. However, the minerals can contribute to spotting on dishes after washing.
The Role of Plumbing Material and Age, Separate From the Source Water
Mineral spotting can be influenced not only by the water’s source but also by the characteristics of your home’s plumbing system. Older plumbing may accumulate mineral deposits, which can flake off and add to spotting even if the incoming water is moderate in mineral content. Materials such as copper, brass, or galvanized pipes interact differently with mineral-rich water, sometimes altering the spotting patterns noticed on glassware and dishes. Therefore, a homeowner's experience of spot-free dishes depends on both the water chemistry recorded in the sampled aquifer and the type, age, and condition of their plumbing system.
A Worked Example: Reading the Record's Median and Range as a Homeowner Would
If your water is typical of the sampled aquifer 112DFSF in CT, your mineral levels might fall around the median of 66.2 mg/L for calcium and magnesium combined. This level can contribute to mineral spots on dishes, particularly glassware, after dishwashing. However, since the range extends up to 1680.0 mg/L, some wells in the area have much higher mineral content, which would cause more pronounced spotting if that were your water. Without testing your own well or tap water, you cannot know your exact concentration, but these figures from the area provide context. Recognizing this range helps set expectations for how challenging spot-free dishes may be based on local groundwater characteristics.
What Distinguishes This Problem from the Two Problems Most Often Confused With It
Mineral spotting is frequently confused with two other common dishwashing issues: detergent residue and improper drying. Detergent residues usually leave cloudy films or streaks rather than distinct mineral spots. Improper drying can cause water spots that evaporate quickly and have a different texture from mineral deposits. Mineral spots result from calcium and magnesium ions left behind after water evaporates, often visible as small, white, or cloudy marks on dishes and glassware. Identifying the correct cause is essential to choosing the right approach for achieving spot-free dishes.
Why Aesthetic Secondary Standards Differ from Health-Based Limits, Applied to This Constituent
The minerals detected in the FIPS 180, aquifer 112DFSF groundwater—calcium and magnesium—are regulated with aesthetic secondary standards rather than health-based limits. These standards focus on taste, staining, and the potential for mineral deposits inside household plumbing or on dishes. Exceeding an aesthetic secondary standard does not mean the water is unsafe; it means it may cause spotting, scaling, or taste issues. The federal record shows no health-based violations for these minerals, so concerns are about how water looks and feels rather than safety. This distinction helps homeowners understand why water that causes spots on dishes is not necessarily harmful.
In summary, the USGS sampling in this CT aquifer shows that mineral concentrations linked to spotting are present but vary widely. Plumbing materials and age also influence spotting. To determine your own water quality regarding dish spotting, testing your water is necessary. The Fleck Spotty Dishes & Glassware System ships ready to configure and is designed to address mineral spotting issues identified in this area’s water records.
Where this information comes from
Source: USGS groundwater sampling. Sampled 2025-11-21. These figures describe groundwater sampled in this area. They are not a test of any individual private well - only a test of that well can establish its own water.
On record: U.S. Geological Survey sampling of Hardness, Ca, Mg in the 112DFSF aquifer (FIPS 180): 69 results from 19 wells, median 66.2 mg/L, range 15.9-1680.0 mg/L; none above any federal threshold
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