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Pennsylvania water profile

Nitrate in Pennsylvania community water systems

Most Pennsylvania community water systems report nitrate below 3 mg/L. The higher results are not spread evenly: they gather in the southeastern limestone valleys, especially Lancaster, Chester, Berks, York and Lehigh. See where the pattern concentrates and what each reporting system measured in the three years from August 9, 2023 to August 9, 2026.

Browse all 1,840 Pennsylvania systems →

Search by the utility or system name shown on a water bill. Example: York Water Co. Private wells are not in this inventory.

99%
of the state’s 1,851 active community water systems have a current result here
1,840
systems with a current nitrate result
11,450,009
people served by those reporting systems
7.9%
of reporting systems at or above 5 mg/L
How to read these numbers Each system is placed into a band by its most recent reported result within a rolling three-year window. The bands describe how strongly human activity, read from nitrate, has marked a water source; they are not a safety verdict. Figures describe system reporting, not nitrate measured at an individual tap.

How Pennsylvania's systems fall across the five bands

Most systems report below 3 mg/L

Natural background
0.00–0.99 mg/L as N
1,009 systems · 5,324,039 served
Human impact likely
1.00–2.99 mg/L as N
450 systems · 3,389,466 served
Human impact clear
3.00–4.99 mg/L as N
235 systems · 2,193,170 served
Health-study range
5.00–9.99 mg/L as N
143 systems · 542,812 served
Above the federal limit
10.00 mg/L and above
3 systems · 522 served

Each system appears in one band only, placed by its most recent reported result in the current three-year window. Counts sit beside people served so a small number of larger systems cannot hide behind a row of tiny ones. Of the 146 systems reporting 5 mg/L or more, 52 stayed at or above 5 across the whole three-year range; the other 94 reached it only on a high sample and otherwise ran lower.

Most recent reading Jul 2026; the typical system was last tested around Feb 2026. 1,670 systems sampled their own water; 170 systems carry a supplier’s result.

The named systems

Every reading here belongs to a utility with a name

Highest recent readings
SystemMost recent resultBandBased onPeople served
Penny Park15.83 mg/LMay 2026a high point — runs lowerAbove the federal limit12 samples51
Mount Rock Manor10.38 mg/LApr 2026a high point — runs lowerAbove the federal limit21 samples350
Pequea Water Coop Assn10.29 mg/LMay 2026Above the federal limit12 samples121
Centre Hall Boro Water Dept9.90 mg/LApr 2026Health-study range13 samples1,900
Wherley Park9.90 mg/LApr 2026a high point — runs lowerHealth-study range11 samples34
Cedar Grove Mobile Home Park9.89 mg/LApr 2026Health-study range11 samples65
West Cocalico Twp Water Auth9.61 mg/LApr 2026a high point — runs lowerHealth-study range25 samples2,430
Christiana Muni Water Auth9.36 mg/LMay 2026a high point — runs lowerHealth-study range24 samples1,100
Largest systems
SystemMost recent resultBandBased onPeople served
Philadelphia Water Department2.88 mg/LJun 2026Human impact likely105 samples1,600,000
Aqua Pa Main System4.00 mg/LJun 2026a high point — runs lowerHuman impact clear74 samples822,600
Pa Amer Water Co-Pittsburgh0.62 mg/LAug 2025Natural background6 samples686,000
Pittsburgh Water & Sewer Auth0.38 mg/LMay 2026Natural background12 samples520,000
Erie City Water Authority0.20 mg/LMay 2026Natural background6 samples220,001

Each result shows its date and what it rests on, so a lone sample is never taken for a settled measurement. A single high sample is not a complete account of what a household drinks.

Where higher nitrate concentrates

Higher results gather in the southeastern limestone valleys

Human impact is clear on drinking water served in 40 of Pennsylvania’s 67 counties. Each is shaded by how many of its systems reported 3.00 mg/L as N or above. Shading counts systems, not severity — a county with many small utilities can outrank one holding a single larger system that reads higher. The table beside the map splits the two bands so that difference stays visible.

PA counties shaded by number of community water systems reporting nitrate at or above 3.00 mg/L as NCounties are shaded by how many community water systems reported nitrate at or above 3.00 mg/L as N in the three years from August 9, 2023 to August 9, 2026. The same counts appear in the table below this map.Lebanon County — 8 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveBeaver County — 0 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLancaster County — 25 systems at 3.00–4.99 mg/L as N; 40 systems at 5.00 mg/L as N or aboveErie County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveBucks County — 14 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveArmstrong County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCarbon County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveBedford County — 2 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveChester County — 28 systems at 3.00–4.99 mg/L as N; 17 systems at 5.00 mg/L as N or aboveNorthumberland County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveFulton County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveNorthampton County — 7 systems at 3.00–4.99 mg/L as N; 10 systems at 5.00 mg/L as N or aboveJuniata County — 1 system at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveWyoming County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLawrence County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveMercer County — 2 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveLuzerne County — 4 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveBlair County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveDelaware County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLehigh County — 16 systems at 3.00–4.99 mg/L as N; 6 systems at 5.00 mg/L as N or aboveSchuylkill County — 2 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveLycoming County — 6 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveColumbia County — 3 systems at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveMonroe County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveUnion County — 0 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveCrawford County — 1 system at 3.00–4.99 mg/L as N; 1 system at 5.00 mg/L as N or aboveWayne County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or abovePotter County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveCumberland County — 9 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveCentre County — 6 systems at 3.00–4.99 mg/L as N; 4 systems at 5.00 mg/L as N or abovePerry County — 2 systems at 3.00–4.99 mg/L as N; 5 systems at 5.00 mg/L as N or aboveSnyder County — 4 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveButler County — 1 system at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveBerks County — 21 systems at 3.00–4.99 mg/L as N; 10 systems at 5.00 mg/L as N or aboveAdams County — 12 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveYork County — 17 systems at 3.00–4.99 mg/L as N; 13 systems at 5.00 mg/L as N or aboveMontgomery County — 12 systems at 3.00–4.99 mg/L as N; 0 systems at 5.00 mg/L as N or aboveHuntingdon County — 0 systems at 3.00–4.99 mg/L as N; 2 systems at 5.00 mg/L as N or aboveDauphin County — 10 systems at 3.00–4.99 mg/L as N; 3 systems at 5.00 mg/L as N or aboveFranklin County — 2 systems at 3.00–4.99 mg/L as N; 6 systems at 5.00 mg/L as N or above
none1–23–56–1112–2526+Number of drinking water systems reporting ≥3.00 mg/L NO₃–N per county as of August 9, 2026

Lancaster leads this layer with 40 reporting systems, followed by Chester, York, Berks. Higher results gather in the southeastern limestone valleys.

Counties with the most systems at or above 3 mg/L as N
County3–4.99≥5Total ≥3
Lancaster254065
Chester281745
Berks211031
York171330
Lehigh16622

Counts use each system's most recent reported result in the current three-year window. A system appears in only one of the two bands.

Find a specific Pennsylvania system

What the statewide pattern says

A carbonate-valley pattern

Pennsylvania's higher nitrate is concentrated in limestone farm valleys — Lancaster County above all — where intensive agriculture and fast groundwater pathways coincide.

Southeastern Pennsylvania is one of the most intensively farmed crop-and-livestock regions in the East. In the carbonate valleys, fractured limestone gives surface nitrogen fast pathways into groundwater. That combination — heavy nitrogen input plus vulnerable aquifer — is the recipe national USGS work associates with higher nitrate in shallow groundwater and drinking-water wells (Nolan and Hitt, 2006).

Pennsylvania's own groundwater studies make the pattern more specific. In the lower Susquehanna basin, wells in agricultural carbonate-bedrock areas exceeded 10 mg/L far more often than wells in other rock settings, and nitrate was strongly correlated with manure application rate (USGS WRI 97-4146). Statewide monitoring later found nitrate above the federal limit in only about 3% of samples, with the highest result in a heavily farmed limestone valley and the greatest vulnerability in the Ridge-and-Valley and Piedmont carbonate areas (USGS SIR 2021-5119).

The Great Valley carbonate work explains why these valleys behave differently. Nitrate there does not necessarily decline with depth, and movement through fractures and solution channels can be rapid and difficult to predict (USGS WRI 95-4099). In Lancaster County dolomite, recharge through fractures and sinkholes changed groundwater nitrate within days of manure application (Gerhart, 1986). Isotope work in the lower Susquehanna traced the nitrogen to manure and, in places, sewage rather than synthetic fertilizer alone (USGS WSP 2497).

The northern half of the state reads differently for a reason that is geological rather than agricultural: in north-central and northeastern Pennsylvania, reducing conditions in the aquifer strip nitrate out, so a low reading there is not evidence that nitrogen never arrived (Cravotta and others, 2021). This is the clearest case on the site of why low nitrate cannot be read as clean water.

The general science — how nitrate moves, why some ground is vulnerable, and why the legacy lingers — is laid out with its sources on Where nitrate comes from.

Questions this page answers

What the Pennsylvania pattern does—and does not—say

Where does nitrate concentrate in Pennsylvania community water systems?

Lancaster leads this layer with 40 reporting systems, followed by Chester, York, Berks. Higher results gather in the southeastern limestone valleys.

Where does nitrate concentrate in Pennsylvania community water systems?

Higher results gather in the southeastern limestone valleys, especially Lancaster, Chester, Berks, York and Lehigh. The 5.00 mg/L-as-N-and-above layer is the most concentrated, led by Lancaster County.

Why is northern Pennsylvania so quiet on this map?

Partly less farming, but also chemistry: in north-central and northeastern Pennsylvania the aquifer is often reducing, and reducing conditions destroy nitrate. A low reading there means nitrate is not present now, not that nitrogen never reached the groundwater (Cravotta and others, 2021).

Does a high public-system result mean a nearby private well is high?

No. It is a local sentinel, not a well-specific result. It shows that nitrogen and a transport pathway have reached groundwater in the area; a certified-lab test is still the only way to know a specific private well.

Can this page say the source is agriculture?

At the zone level, yes — carefully. In Pennsylvania's limestone farm valleys the supported reading is agricultural with a manure-heavy input budget, and isotope work supports it. The evidence does not resolve manure versus fertilizer versus septic at each individual system.

Does a high public-system result mean a nearby private well is high?

No. It is a local sentinel, not a well-specific result. It shows that nitrogen and a transport pathway have reached groundwater in the area; a certified-lab test is still the only way to know a specific private well.

Sources and provenance

What this page rests on

  1. NitrateSmart inventory: 1,840 Pennsylvania community water systems with a current nitrate result in the three years from August 9, 2023 to August 9, 2026. Figures count people served by reporting systems, not measured tap exposure.
  2. Nolan BT, Hitt KJ (2006). Vulnerability of Shallow Groundwater and Drinking-Water Wells to Nitrate in the United States. Environmental Science & Technology 40(24):7834–7840.
  3. Lindsey BD, Loper CA, Hainly RA (1997). Nitrate in ground water and stream base flow in the lower Susquehanna River Basin. USGS Water-Resources Investigations Report 97-4146.
  4. Conlon MD (2021). Ambient groundwater quality of the shallow aquifer system in Pennsylvania, 2015–19. USGS Scientific Investigations Report 2021-5119.
  5. Ferrari MJ, Ator SW (1995). Nitrate in ground water in the Great Valley carbonate subunit in south-central Pennsylvania. USGS Water-Resources Investigations Report 95-4099.
  6. Gerhart JM (1986). Ground-water recharge and nitrate beneath a manured field in Pennsylvania. Groundwater 24(4).
  7. USGS (2002). Stable isotopes of carbon, nitrogen, and sulfur to identify nitrogen sources in the lower Susquehanna River Basin. USGS Water-Supply Paper 2497.
  8. Cravotta CA III, Senior LA, Conlon MD (2021). Groundwater quality in relation to geologic and hydrogeologic setting in north-central and northeastern Pennsylvania. Applied Geochemistry 134:105149.
  9. Dubrovsky NM, and others (2010). Nutrients in the Nation's Streams and Groundwater, 1992–2004. USGS Circular 1350.