Perchlorate in New York Drinking Water
Ranked by max perchlorate detected (µg/L) · UCMR 1 data (2001–2005) · Data from EPA SDWIS & UCMR
Perchlorate in New York: what the data shows
New York has 15 cities with perchlorate data from the EPA's UCMR 1 program (2001–2005). Perchlorate exceeded California's 6 µg/L MCL in 13 of those cities. The state average max detected level is 11.00 µg/L. Note: this is the most recent national perchlorate monitoring dataset; UCMR rounds 2–5 did not include perchlorate. Perchlorate (ClO4⁻) is an oxidizing salt used historically in solid rocket propellants, fireworks, road flares, and certain explosives. It enters drinking water primarily from defense and aerospace contamination sites, fireworks manufacturing, and some natural deposits in arid regions. It is highly soluble and very mobile in groundwater. Perchlorate interferes with thyroid iodide uptake and hormone production, with potential effects on fetal and infant brain development. There is no federal MCL — the EPA proposed regulating perchlorate at 56 µg/L in 2008, withdrew the rule in 2020, and has not finalized a federal limit. California's MCL is 6 µg/L, Massachusetts is 2 µg/L. Reverse osmosis and ion exchange are effective treatments.
Cities exceeding CA MCL: 6 µg/L · MA MCL: 2 µg/L (no federal MCL)
Perchlorate data across New York
Each dot is a city with UCMR 1 perchlorate testing data. Cities above the 15 µg/L reference level are highlighted. Size reflects population served.
Top 10 cities by perchlorate level in New York
All New York cities ranked by perchlorate level
| # | City | Level | Level | Over CA MCL? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Hempstead (T) | 14.00 µg/L | Over CA MCL | 9 | F | |
| 2 | Westbury (V) | 14.00 µg/L | Over CA MCL | 2 | A- | |
| 3 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 11 | D | |
| 4 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 5 | C+ | |
| 5 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 5 | B+ | |
| 6 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 5 | B | |
| 7 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 6 | B+ | |
| 8 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 7 | B- | |
| 9 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 3 | C | |
| 10 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 11 | B- | |
| 11 | Smithtown (T) | 12.10 µg/L | Over CA MCL | 3 | A- | |
| 12 | Oyster Bay (T) | 11.00 µg/L | Over CA MCL | 14 | B- | |
| 13 | Hempstead (T) | 8.87 µg/L | Over CA MCL | 14 | D | |
| 14 | Garden City (V) | 4.20 µg/L | No | 5 | A- | |
| 15 | Glen Cove (C) | 4.02 µg/L | No | 4 | B+ |
Frequently asked questions about perchlorate in New York
Is perchlorate in New York tap water harmful?
Perchlorate interferes with thyroid hormone production by blocking iodide uptake, which is a particular concern for fetuses, infants, and people with hypothyroidism. 13 cities in New York had perchlorate above California's 6 µg/L MCL in UCMR 1 testing (2001–2005). There is no federal MCL.
Why doesn't the EPA regulate perchlorate federally?
The EPA proposed a federal perchlorate MCL of 56 µg/L in 2008 and reversed course in 2020, citing insufficient evidence of widespread risk above that threshold. Critics — including pediatric and thyroid health groups — argue that the 6 µg/L California MCL or 2 µg/L Massachusetts level is more health-protective. Federal regulation remains pending. UCMR 1 (2001–2005) is the most recent systematic national perchlorate dataset.
How can I remove perchlorate from my drinking water?
Reverse osmosis is highly effective (90%+ removal). Anion exchange systems also work well. Standard activated carbon filters are NOT effective against perchlorate. If you live near a former military, aerospace, or fireworks-manufacturing site, periodic perchlorate testing of well water is warranted.