Nassau County, NY Water Quality

About Nassau County water

How water works in Nassau County

Nassau County ranges from dense villages and downtowns to lower-density suburban and, on the East End, semi-rural areas. Almost everyone is served by a public water district or utility drawing on the Long Island aquifer, though some outlying properties still use private wells. Because the aquifer is the sole source of drinking water, what reaches it at the surface directly shapes water quality.

Here, drinking water is pumped entirely from local groundwater — the federally designated Long Island sole-source aquifer system (Upper Glacial, Magothy, and Lloyd aquifers). There is no surface-water supply here, which makes the aquifer's protection central to water quality.

Your provider

Water system providers in Nassau County

In Nassau County, water is supplied by dozens of local public water districts and village systems, plus New York American Water (now Liberty Utilities) in several areas. One address can still fall within more than one system, so confirm the provider on a recent bill or with the official lookup tools below.

Water systems (federal records)

Community water systems serving Nassau County

Federal EPA drinking-water records list 40 active community water systems serving Nassau County, together reported to serve about 1,354,175 people. The largest are shown below (by population served). Click a PWS ID for that system's federal report.

…and 25 more, mostly smaller community systems. Full federal records for every system are on EPA ECHO.

Source: EPA Safe Drinking Water Information System (SDWIS), pulled July 2026. Population and connection figures are SDWIS-reported estimates. This lists community systems only — it excludes private wells and transient systems. Confirm the exact system for an address on a water bill.

Compliance

Violations and notices in Nassau County

Of the 40 community water systems serving Nassau County, federal EPA records show 8 with at least one health-based violation on record over the years. A violation can range from a monitoring/reporting lapse to an exceedance that has since been resolved — open a system's federal report (linked in the table above) or its current Consumer Confidence Report for the specifics and current status.

Water characteristics

What Nassau County water is typically like

Long Island groundwater is generally soft to moderately hard but varies by well field and depth. Because the aquifer is the sole source, it is sensitive to what happens at the surface — road salt, fertilizer, and industrial legacy contamination can all reach it, which is why nitrate, 1,4-dioxane, and PFAS monitoring are prominent here.

Regional patterns are a general guide only — hardness, iron, and other traits vary by specific system and well. Your CCR (or a well test) is the authoritative source for your address.

Local water-quality context

Nassau County: PFAS and 1,4-dioxane in the aquifer

As a sole-source aquifer community, Nassau County has been central to New York's nation-leading drinking-water standards for 1,4-dioxane, PFOA, and PFOS. Many districts have installed advanced oxidation (for 1,4-dioxane) and granular activated carbon (for PFAS) at affected well fields. Some South Shore areas also see naturally elevated iron and manganese.

This is documented regional background, not an address-level test result. Always confirm current conditions in your provider's latest Consumer Confidence Report (CCR) or, for a private well, with your own certified lab test.

Reported contaminant levels

Liberty Utilities New York - Lynbrook — reported levels (2024 report)

Selected regulated contaminants from this system's official Consumer Confidence Report. "Below/At/Above" compares the reported value to its limit; it does not replace the utility's formal compliance determination.

Values transcribed from the official CCR (source ↗) as a first-pass reading — always confirm against the full report, which lists every monitored contaminant, ranges, and footnotes. Lead/copper are 90th-percentile action-level results. This is a partial panel; absence of a contaminant here does not mean it wasn't tested.

PFAS monitoring (EPA UCMR5)

PFAS monitoring results in Nassau County

Under the EPA's fifth Unregulated Contaminant Monitoring Rule (UCMR5), 33 water systems in Nassau County tested for 29 PFAS compounds and lithium in 2023–2025. Of those, 22 had at least one PFAS detection, and 13 had a detection of PFOA or PFOS (the two PFAS New York regulates most strictly).

How to read this: These are occurrence-monitoring results, not compliance determinations. New York's enforceable limit (MMCL) is 10 ppt each for PFOA and PFOS; a monitoring result above that is a signal to look closer, not automatically a violation — and a system may have added treatment or changed sources since it was sampled. Values are the highest detected at any sampling point, in parts per trillion (ppt). Always check the system's current Consumer Confidence Report for its latest status. Source: EPA UCMR5 (data collected 2023–2025). See PFAS explained and NY drinking water standards.

Read the fine print

What these records don't show

The system and compliance records above come from federal data. Some things people ask about are not captured here and should be confirmed directly:

• Contaminant levels at your tap. Actual values (lead, PFAS, nitrate, disinfection byproducts, etc.) come only from your system's Consumer Confidence Report or your own well test — we do not publish or estimate them.
• Water hardness. Not in the federal system records. Ask your utility for the CCR hardness value or use a home hardness test. See our hard-water guide.
• Taste, odor, color, and staining. These aesthetic issues are not standardized here; your CCR's secondary-contaminant notes and your own observations are the best guide.
• Year-over-year change. We don't track how a system's results changed from last year — compare this year's CCR to last year's using the report links.

Detailed local guides

Town & city water guides in Nassau County

Deeper guides naming the specific water provider and local context for each place:

Mineola · Hempstead · Long Beach · Freeport · Garden City · Levittown · Hicksville · Glen Cove · Valley Stream · Rockville Centre · Massapequa · Westbury · Uniondale · Baldwin · Oceanside · Wantagh · Bethpage · Franklin Square · Farmingdale · Great Neck · Port Washington · Manhasset · Roslyn · Merrick · Bellmore · East Meadow · Elmont · Lynbrook · Plainview · Syosset · Seaford · New Hyde Park

Find your report

How to find your water provider and report

1. Check a recent water bill for your water system or district name.
2. Look up that system and its most recent Consumer Confidence Report (CCR) using the official tools below.
3. On a private well? A CCR won't apply — see our private well testing guide.

• NYSDOH Drinking Water Protection Program
• EPA ECHO · EPA SDWIS federal reports
• Our step-by-step CCR finder guide

Confirm it's your water

Make sure a report is actually yours

1. Find the provider name and PWS ID printed on your water bill — a town name or ZIP alone is not enough to identify the system.
2. Match that PWS ID to the systems table above (or search it on EPA ECHO).
3. Open that system's current CCR for the official results and any notices.
4. For a point-of-use concern (especially lead), use a certified laboratory test for your specific tap — the system-wide report can meet standards while an individual older home does not.

Lead & older homes

Lead and service lines in Nassau County

Lead is almost never in the water leaving a treatment plant — it typically enters from a lead service line or older home plumbing. A system-wide CCR can meet the lead action level while an individual older home shows a higher result at the tap. New York requires public water systems to inventory their lead service lines, so ask your utility for its inventory, and confirm your own tap with a certified laboratory test. See our lead & copper guide and utility report vs. home tap test.

Communities

Cities, towns, villages, and hamlets in Nassau County

Local guidance in Nassau County is most relevant to these cities, towns, villages, and hamlets:

• Mineola
• Hempstead
• Long Beach
• Freeport
• Garden City
• Levittown
• Hicksville
• Glen Cove
• Valley Stream
• Rockville Centre
• Massapequa
• Westbury
• Uniondale
• Baldwin
• Oceanside
• Wantagh
• Bethpage
• Franklin Square
• Farmingdale
• Great Neck
• Port Washington
• Manhasset
• Roslyn
• Merrick
• Bellmore
• East Meadow
• Elmont
• Lynbrook
• Plainview
• Syosset
• Seaford
• New Hyde Park

Representative ZIP codes

A sample of ZIP codes in Nassau County (not a complete list; one ZIP can span multiple systems):

• 11501
• 11530
• 11550
• 11553
• 11554
• 11556
• 11557
• 11558
• 11559
• 11560
• 11561
• 11563
• 11565
• 11566
• 11568
• 11570
• 11572
• 11575
• 11576
• 11577
• 11579
• 11580
• 11581
• 11590
• 11596
• 11598
• 11701
• 11710
• 11714
• 11720
• 11725
• 11726
• 11732
• 11735
• 11740
• 11746
• 11753
• 11756
• 11758
• 11762
• 11765
• 11783
• 11793
• 11801
• 11803
• 11804
• 11040
• 11042
• 11050
• 11021
• 11023
• 11024
• 11030

Improve your water

Common Nassau County home water steps

Authoritative resources

Official & academic water resources for Nassau County

For primary data and research beyond this guide, these New York agencies and universities are the authoritative sources:

• NYSDOH — Drinking Water Protection Program
• NYSDEC — Water
• USGS — New York Water Science Center
• Cornell University — NYS Water Resources Institute: Drinking Water
• Stony Brook University — NYS Center for Clean Water Technology

FAQ

Frequently asked questions

Who provides drinking water in Nassau County?

dozens of local public water districts and village systems, plus New York American Water (now Liberty Utilities) in several areas. Federal records list 40 active community water systems in the county. Check a recent water bill or the lookup tools to confirm the exact system serving your address.

How do I find my water quality report in Nassau County?

Every community water system must publish an annual Consumer Confidence Report (CCR). Identify your provider first, then request its current CCR from the provider or through NYSDOH. Private wells are not covered by a CCR and must be tested independently.

Is Nassau County water hard or soft?

Long Island groundwater is generally soft to moderately hard but varies by well field and depth.

Are there water-quality violations in Nassau County?

Federal EPA records show 8 of the county's 40 community water systems with a health-based violation on record over the years; open a system's federal report or current CCR for status.

Does this page publish local test results?

No. We publish the systems, sources, and compliance records that come from federal data, but not address-level contaminant values — those come only from each provider's official CCR and the NYS Department of Health.

Last reviewed: July 2026