Data & Methodology — Polk County Well Water

Contaminant Data — All Analytes

2617 well testing events on record, covering 22 analytes. Data spans 1941 to 2025.

Contaminant	Samples	Years	Detection Rate	vs. Limit	vs. FL Avg
PFOS municipal	101	2023–2025	24%	151% of limit	↓ 28% below
Iron	1792	1959–2025	96%	7% of limit	↓ 97% below
Nitrate	431	1959–2019	71%	4% of limit	~ typical
Sulfate	2169	1941–2025	98%	4% of limit	↓ 85% below
Manganese	1695	1972–2025	92%	4% of limit	↓ 83% below
PFOA municipal	101	2023–2025	8%	145% of limit	~ typical
Chloride	2281	1941–2025	100%	5% of limit	↓ 90% below
Fluoride	1743	1959–2025	99%	8% of limit	~ typical
Radon	11	2002–2019	100%	21% of limit	↓ 27% below
Nitrite	363	1972–2024	39%	0% of limit	↓ 76% below
HFPO-DA (GenX) municipal	101	2023–2025	0%	—	—
Uranium	32	1974–2019	66%	1% of limit	~ typical
Lead	291	1972–2024	37%	1% of limit	↓ 58% below
PFHxS municipal	101	2023–2025	12%	36% of limit	↓ 31% below
PFNA municipal	101	2023–2025	0%	—	—
pH	2086	1941–2025	100%	—	~ typical
Sodium	2017	1955–2025	99%	—	↓ 88% below
Hardness	582	1941–2019	100%	—	↓ 49% below
Total Coliform	158	1987–2025	98%	—	~ typical
E. coli	68	2002–2025	97%	—	~ typical
Fecal Coliform	90	1987–2021	97%	—	~ typical
PFBS municipal	100	2023–2025	11%	—	~ typical

Distribution shows the share of samples in each concentration band relative to the EPA Maximum Contaminant Level (MCL): Low = below half the MCL, Moderate = between half and the MCL, High = above the MCL. Analytes without an MCL (e.g. sodium, pH) show — in the limit columns. State average is based on county median values across FL.

Data Coverage & Gaps

Well-sampled analytes (15+ samples)

Iron 1792 samples
Nitrate 431 samples
Sulfate 2169 samples
Manganese 1695 samples
Chloride 2281 samples
Fluoride 1743 samples
Nitrite 363 samples
Uranium 32 samples
Lead 291 samples
pH 2086 samples
Sodium 2017 samples
Hardness 582 samples
Total Coliform 158 samples
E. coli 68 samples
Fecal Coliform 90 samples

Limited data (<15 samples) — interpret with caution

Radon 11 samples

No private-well PFAS data for Polk County

We have no private well sampling data for PFAS compounds (PFOA, PFOS, PFNA, and related chemicals) in Polk County. PFAS has been detected in local public water systems (UCMR 5 data) — indicated by the "municipal" badge in the table above — but this does not directly indicate private well contamination. PFAS testing for private wells requires a dedicated lab panel (~$300–$500). If you are near a military base, airport, or industrial site, consider testing proactively. Learn more about PFAS →

Public vs. Private Water in Polk County

401 Active public water systems

672,540 Residents on public water

Public water systems in Polk County are regulated by the EPA and must test and report contaminant levels. Private well owners are responsible for their own testing — there is no routine monitoring of private wells by any government agency.

CDC Health Outcome Correlations

Where contaminants detected in Polk County have established associations with specific health outcomes, we cross-reference CDC PLACES county-level prevalence data. This is a contextual signal, not a causal claim.

Contaminant	Associated Condition	Polk County Prevalence	FL Average	Source Year
Nitrate	Cancer prevalence	7.4%	6.8%	2020

Data Sources

This report aggregates data from the following public databases:

Water Quality Portal (WQP) — groundwater sample results for Polk County from EPA, USGS, and state agencies. Browse WQP data →
EPA Safe Drinking Water Information System (SDWIS) — public water system inventory used to estimate the share of residents on private wells. Browse SDWIS →
Census ACS 5-Year Estimates — well and cistern household counts (variable DP04_0074E) used to calculate the private-well percentage for Polk County. Census data explorer →
USGS Aquifer Atlas — principal aquifer type underlying Polk County, which informs which contaminants are geologically likely. USGS Aquifer Atlas →
EPA UCMR 5 (2023–2025) — PFAS occurrence data from public water systems, used as a proxy indicator for aquifer PFAS exposure. Rows marked "municipal" in the table above come from this source. About UCMR 5 →
EPA Toxics Release Inventory (TRI) — industrial facility chemical releases near Polk County, used in contamination risk scoring. TRI Explorer →
EPA Superfund NPL — National Priorities List sites in or near Polk County, used in contamination risk scoring. Superfund site search →
CDC PLACES — county-level health outcome prevalence (kidney disease, cancer, heart disease) correlated with detected contaminants. About CDC PLACES →

Methodology

Raw records are downloaded from the Water Quality Portal and normalized to µg/L (ppb). Records are deduplicated by sample ID and date, and certified outliers are excluded. Analyte names are mapped to EPA canonical forms. Detection rates, distribution bands, and MCL comparisons are computed from the normalized dataset.

Distribution bands use the EPA Maximum Contaminant Level as the threshold: concentrations below 50% of the MCL are classed as Low, between 50% and 100% as Moderate, and above 100% as High. For analytes without an MCL (sodium, hardness, pH), distribution is not computed.

State comparison uses the median of county median values across all counties in FL with at least one sample for that analyte.

Last updated: 2026-08-12

Full methodology →