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Federal water data

County water report

Nassau County Water Report

Drinking-water compliance, watershed health, monitoring records, and river conditions for Nassau County, New York.

Water grade

B

Water score

68.8

State rank

#5

of 57

Health violations

20

EPA SDWIS, 5-year lookback

Watershed impaired

Not reported

EPA ATTAINS coverage varies by state

Monitoring sites

267

75,454 recent measurements

Live streamflow

17%

MASSAPEQUA CREEK AT MASSAPEQUA NY

Water at a glance

Key Water Indicators for Nassau County

EPA SDWIS

Safety Grade

B

Score: 68.8 / 100

EPA SDWIS

Active Violations

20

5-year health-based lookback

EPA ATTAINS

Watershed Health

Not reported

Coverage varies by state

USGS NWIS

Streamflow Snapshot

17% of mean

MASSAPEQUA CREEK AT MASSAPEQUA NY

EPA WQP

Monitoring Sites

267

75,454 recent readings

Source: EPA SDWIS · Safe Drinking Water Information System

Drinking Water Compliance

Compliance grade

B

Based on EPA SDWIS compliance history.

Water score

Higher scores indicate cleaner recent compliance records.

68.8/100

Health violations

20

Health-based violations

Violations per 100K served

1.5

Population-normalized SDWIS rate

Editorial analysis

Understanding Nassau County’s Water

Drinking Water Quality Overview

EPA SDWIS

Nassau County earns a B grade for drinking water quality, scoring 68.8 out of 100. Over the past five years, EPA SDWIS records 20 health-based violations — a pattern that public water utilities are required to disclose and correct.

River & Streamflow Status

USGS NWIS

USGS NWIS gauge data (as of 2026-05-14T14:00:00.000-05:00) puts MASSAPEQUA CREEK at 1.5 cfs — well below its long-term average at 17% of mean — low-flow conditions worth noting for water-dependent ecosystems. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

Monitoring Network

EPA WQP

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Nassau County has extensive coverage with 267 active monitoring sites with 75,454 recent measurements on record. Predominant monitoring categories include physical and nutrient. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.

Editorial advisory

What the data suggests for Nassau County

Water Verdict

Nassau County receives a fair water quality assessment with a grade of B and a score of 68.8 out of 100. The water supply meets baseline federal standards, but there may be periods of elevated contaminant levels or infrastructure concerns worth monitoring.

Violation Context

Nassau County has recorded 20 health-based violations, indicating multiple instances where federal contaminant limits or treatment requirements were not met. At 1.5 violations per 100,000 people served, this rate is relatively low compared to many U.S. counties.

Consumer Guidance

Tap water in Nassau County meets baseline safety standards, though the compliance record shows some violations worth watching. Nassau County's drinking-water compliance score is 68.8 out of 100. The violation rate for Nassau County is 1.5 per 100,000 people served. Running tap water for 30 seconds before drinking can reduce any localized lead exposure from household plumbing. Requesting your utility's most recent Consumer Confidence Report is the fastest way to identify which specific contaminants were flagged. With 267 active water-quality monitoring sites in Nassau County, data coverage is strong. A pipeline streamflow snapshot from the MASSAPEQUA CREEK gauge is also available on this page.

Regional Context

Nassau County has better water quality than the average county in New York. Its water score is 28.7 points higher than the state average, indicating stronger water system performance relative to neighboring counties.

Advisory text summarizes county-level public records and is not a replacement for your utility's current Consumer Confidence Report or direct local notices.

Contaminants & Resources

Key issues flagged in Nassau County's water environment

Official EPA Resources for Nassau County

EPA How's My Waterway

Interactive watershed health data for Nassau County

EPA ECHO: Drinking Water Systems

Search water utilities and violation records for Nassau County

Consumer Confidence Reports (NY)

Annual water quality reports from utilities in New York

Past 5 years

Water Quality Monitoring

Monitoring Sites

267

Active in the past 5 years

Measurements Recorded

75K

75,454 total readings

Most Measured

  • Physical
  • Nutrient
  • Microbiological

Categories measured most frequently

Data from the EPA Water Quality Portal (WQP), aggregating monitoring records from federal, state, and tribal sources. Each measurement represents a single sample analyzed for a specific characteristic (e.g., E. coli, pH, dissolved oxygen, nitrogen).

Live USGS Streamgage

River & Stream Conditions

Current Discharge

1.50cfs

May 14, 7:00 PM UTC

vs Long-Term Average

17%

Well below typical

Primary Streamgage

MASSAPEQUA CREEK AT MASSAPEQUA NY

USGS site
01309500
Drainage area
38.6 sq mi
Long-term mean
8.62 cfs

One representative streamgage (the one with the largest drainage area in the county). Many counties have multiple gauges; this view summarizes the primary one. The long-term mean is the full-record annual average; the percent-of-typical value compares the latest reading against that average.

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Water Cost Estimate

3

3 people  ·  ~225 gal/day

Annual Total

$558

Monthly

$47

Water Bill

$558/yr

Filter Cost

$0/yr

Safety Grade for Nassau County:C — Moderate

Some violations or watershed impairment detected.

Estimates use the national average residential water rate ($0.0068/gal, EPA/AWWA 2023) and EPA WaterSense per-person consumption baseline (75 gal/person/day). Actual bills vary by utility, usage tier, and local infrastructure fees. For informational purposes only.

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Frequently Asked Questions

What is the water quality in Nassau County, New York?
Nassau County, New York has a drinking-water quality grade of B with a score of 68.8/100, based on EPA SDWIS compliance data. The county has 20 health-based drinking water violations over the past 5 years. Watershed health, monitoring records, and streamflow snapshots are reported separately on this page.
Are there any water violations in Nassau County?
Nassau County has 20 health-based drinking water violations recorded by the EPA over the past 5 years. Health-based violations indicate instances where contaminant levels exceeded EPA Maximum Contaminant Levels (MCLs). Violations may have been resolved — check with your local water utility for current status.
How much water-quality monitoring happens in Nassau County?
EPA's Water Quality Portal records 75,454 measurements from 267 monitoring sites in Nassau County over the past five years. The most frequently measured characteristic groups are Physical, Nutrient, Microbiological. Each measurement is a single sample analyzed for one characteristic (E. coli, pH, dissolved oxygen, etc.). High monitoring density means more scientific evidence behind any reported signal — it does not by itself indicate water quality.
What's happening with rivers in Nassau County right now?
Nassau County's primary USGS streamgage on the MASSAPEQUA CREEK has a pipeline snapshot of 1.5 cubic feet per second — 17% of the long-term mean of 8.62 cfs. This is well below typical — often a signal of drought stress on source water. For the latest gauge feed, visit waterdata.usgs.gov.
How does Nassau County water compare to the New York average?
Nassau County's SDWIS water quality score of 68.8/100 is higher than the New York state average of 40.1. The average water quality grade across New York is D, based on data from 57 counties with available SDWIS data.
Is tap water safe to drink in Nassau County?
Based on EPA SDWIS data, Nassau County has a water quality grade of B (68.8/100). This indicates good to excellent water quality with strong SDWIS compliance. The grade speaks to the public water system, not the watershed — for watershed-level concerns, see the Watershed Health zone. For the most up-to-date information, contact your local water utility or review your Consumer Confidence Report (CCR).
Why does Nassau County have so many water violations?
Nassau County has 20 health-based drinking water violations on record from the EPA SDWIS database. A higher violation count can result from aging infrastructure, underfunded water utilities, agricultural runoff contamination, or industrial pollution. Counties with more water systems may also see more violations simply due to scale. Residents concerned about water quality should consider independent water testing and home filtration systems.
How does Nassau County rank for water quality in New York?
Nassau County ranks #5 out of 57 counties in New York by SDWIS water quality score (1 = best). With a score of 68.8/100, it falls in the top third of counties statewide. The ranking reflects EPA SDWIS compliance only — not watershed impairment, monitoring density, or streamflow, which are tracked separately on this page.

Counties with Similar Water Quality

Monroe County

New York

B

68.6

Water score

St. Lawrence County

New York

B

68.6

Water score

Chemung County

New York

B

69.5

Water score

Data Sources

Drinking-water compliance data from the EPA Safe Drinking Water Information System (SDWIS) via the ECHO enforcement database. Scores reflect compliance history and health-based violation counts.

Water-quality monitoring counts from the EPA Water Quality Portal (WQP), federated USGS, EPA, and state agency sampling records over a rolling 5-year window.

Live streamflow from the USGS National Water Information System (NWIS), continuous discharge measurements from the largest-drainage gauge in each county, compared against the full-record long-term annual mean.

Disclaimer: This data is informational only. It is not health, legal, or professional advice. For concerns about your specific water supply, contact your local water utility.

By Evan Brooks, Data EditorUpdated Reviewed by Evan Brooks, Data Editor

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