Government data from the EPA on the Arecibo Urbano public water system in Puerto Rico shows that, as of 2024, levels of various per- and polyfluoroalkyl substances (PFAS)—often called 'forever chemicals'—have been measured but do not exceed federal health-based maximum contaminant levels (MCLs). This page helps clarify what the publicly reported PFAS monitoring means, what it does not establish, and how homeowners can interpret these findings when selecting water treatment technologies.
Firefighting Foam, Textile Finishing, and Landfill Sources: Which Fits This Region's Record
PFAS substances can enter water systems from multiple sources including firefighting foam residues, textile finishing facilities, and landfill leachate. In the Arecibo Urbano water system record, 44 samples were tested between April 2024 and January 2025 for a range of fluorinated compounds. The detection pattern in this region shows virtually no measurable presence of compounds typically associated with large-scale industrial or firefighting foam contamination, as evidenced by the absence or near-absence of PFOA, PFHxS, PFNA, PFBS, and other long-chain PFAS above reporting limits.
Which Fluorinated Compounds in This Record Now Carry a 2024 Federal MCL and Which Do Not
In 2024, the federal government established MCLs for several PFAS compounds. For Arecibo Urbano, these include:
- PFOA (perfluorooctanoic acid) with an MCL of 4.0 nanograms per liter (ng/L or parts per trillion, ppt)
- PFOS (perfluorooctanesulfonic acid) with the same MCL of 4.0 ng/L
- PFHxS (perfluorohexanesulfonic acid), PFNA (perfluorononanoic acid), and HFPO-DA measured but with higher MCLs or none yet set.
In this system, PFOA was never detected above the reporting limit, while PFOS was detected once just above detection but well below the MCL threshold, indicating compliance but measurable presence. Other compounds were below detection limits or not detected at all.
How the UCMR5 Survey Differs from UCMR3 in Which Compounds It Looked for and at What Level
The current data comes from the EPA's Unregulated Contaminant Monitoring Rule 5 (UCMR5) program, a federal survey designed to identify emerging contaminants, including a broader suite of PFAS than earlier surveys. Compared with UCMR3, which focused on fewer PFAS at higher detection limits, UCMR5 uses more sensitive methods, lowering reporting levels to fractions of a nanogram per liter, allowing detection of trace concentrations previously unmeasurable. This means that the apparent low-level detections in Arecibo Urbano represent improved analytical capability rather than necessarily increased contamination.
A Worked Example: Reading the Record's Median and Range as a Homeowner Would
For PFOS in Arecibo Urbano, the median detected concentration when detected is 0.0044 micrograms per liter (µg/L), or 4.4 ng/L, just slightly above the reporting limit of 0.004 µg/L but still below the MCL of 4.0 ng/L. Since only one sample out of 44 detected PFOS, the median of detections is a limited statistic but shows that occasional trace levels may occur. For all other PFAS compounds, no detections above reporting limits were found, implying that typical levels are below these thresholds. Note that these figures describe the public water system overall, not any single household’s water.
How Many Samples and Wells Stand Behind the Figures, and What a Small Sample Means
The data is based on 44 samples taken from the public water system's distribution points and source wells. While this sample size provides an overview, it does not capture variability at every location or household. Smaller sample sizes mean occasional detections may not represent stable conditions or predict individual home water quality. Homeowners concerned about PFAS should consider testing their own tap water in addition to reviewing public records.
What 'Detected', 'Median', and 'Range' Mean in the Sampling Record on This Page
'Detected' means the laboratory instrument found PFAS at or above the reporting limit, not that the concentration exceeds health-based standards or is unsafe. 'Median' refers to the middle value among detected concentrations. 'Range' indicates the minimum and maximum detected levels. These statistics are tools for understanding regional water quality trends but do not by themselves diagnose any individual household’s water safety or treatment needs.
Choosing between water treatment equipment classes to address PFAS should consider the presence and type of PFAS found, daily water demand, and technology efficacy documented for reducing per- and polyfluoroalkyl substances. The C-Series PFAS Forever Chemicals Filter is designed specifically to reduce a broad spectrum of fluorinated compounds and ships ready to configure for residential use.
In summary, the Arecibo Urbano sample record shows low to very low PFAS concentrations well below federal limits, with a single low-level PFOS detection. This information guides homeowners in Puerto Rico considering PFAS filters but emphasizes the value of individual water testing. Selecting the right treatment involves understanding local system data, testing household water, and choosing proven filtration technology.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2025-01-26. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR5 monitoring (2023-2025) for ARECIBO URBANO (PR0002652), PR: 440 results across 10 listed contaminants, 1 detections above the reporting level; 1 results above a 2024 federal MCL