The Aguadilla public water system in Puerto Rico serves thousands of residents through a network of water connections drawing from local sources. Measuring PFAS — per- and polyfluoroalkyl substances, sometimes called 'forever chemicals' — in drinking water involves detecting extremely low concentrations, captured in nanograms per litre (ng/L), equivalent to parts per trillion (ppt). These measurements help inform households considering which class of water treatment best fits their needs.
Why PFOA and PFOS Are Measured in Nanograms per Litre
Precision of four decimal places in reporting
PFAS compounds such as PFOA and PFOS exist at trace levels, often in the range of thousandths of a microgram per litre. Reporting to four decimal places (e.g., 0.0040 µg/L) allows the federal monitoring programs to detect sources of contamination with great sensitivity, enabling early awareness of potential issues without implying a health risk.
Differences Between UCMR5 and UCMR3 Monitoring
Wider scope of compounds in current surveys
The EPA’s UCMR5 sampling in Aguadilla (2023–2025) expands on earlier UCMR3 monitoring by including additional fluorinated compounds. This survey detects a broader range of PFAS variants at low reporting levels, offering more comprehensive data on the presence of these substances in the public water supply.
Lower detection limits for certain substances
The reporting levels for compounds like PFHxS and PFBS in UCMR5 are stricter than in previous rounds, allowing identification of even minor presences that were previously undetectable.
2024 Federal Maximum Contaminant Levels (MCLs) Status
PFAS compounds with federal MCLs
For 2024, the EPA has established federal maximum contaminant levels for several PFAS compounds. These include:
- PFOA: 4.0 ng/L
- PFOS: 4.0 ng/L
- PFHxS: 10 ng/L
- PFNA: 10 ng/L
- HFPO-DA (GenX): 10 ng/L
Detected substances without a current MCL
Other fluorinated compounds, such as PFBS, PFHxA, PFPeA, and PFBA, have been detected in Aguadilla’s system but do not currently have federal MCLs, meaning no enforceable concentration limits exist for them yet.
Aesthetic Secondary Standards Versus Health-Based Limits
Purpose of secondary standards
Regulatory guidelines include secondary standards to address taste, odor, staining, and corrosivity related to water constituents. These are separate from primary health-based standards and do not indicate a health risk if exceeded.
Relevance to PFAS levels
Though some PFAS can influence water aesthetics, federal MCLs specifically target health protection. Detected concentrations in Aguadilla remain well below or close to these health-based thresholds, reinforcing the absence of recorded violations.
Local Likely Sources of PFAS
Potential regional contributors
Common regional sources of PFAS include historical use of firefighting foams, textile finishing operations, and landfill leachates. No EPA health-based violations have been recorded in Aguadilla, indicating control measures or low-impact presence.
How PFAS Reach Groundwater and Distribution Systems
Migration pathways
PFAS compounds can enter groundwater through surface runoff, infiltration of contaminated sites, or leaching from landfills. From there, they may move into public water distribution. Local hydrogeology and infrastructure impact the extent of this movement.
Role of system-wide sampling
EPA’s UCMR5 monitoring samples the system at various points to capture overall water quality trends rather than individual home levels, which can vary.
What Not to Conclude From Area Data
Individual testing remains essential
While Aguadilla’s public water system data shows no health-based violations for PFAS, these findings do not confirm the concentration in your home's tap water. Only a specific test of your water supply can determine this.
Detections are not violations
A detection above the reporting level does not mean a violation of standards or unsafe water; it simply means the substance was measurable at low levels by sensitive instruments.
For residential treatment decisions, considering a Fleck PFAS Forever Chemicals Filter can help address 'forever chemicals' commonly found in regional water sources. This system ships ready to configure and is designed to reduce PFAS concentrations effectively, complementing the data available about your community’s water.
Where this information comes from
Source: EPA SDWIS public water system record. Sampled 2025-12-17. These figures describe the public water system's record, not the plumbing inside any individual building.
On record: EPA UCMR5 monitoring (2023-2025) for AGUADILLA (PR0003293), PR: 320 results across 10 listed contaminants, 20 detections above the reporting level; 5 results above a 2024 federal MCL