Agricultural runoff and septic contamination — tracked at public water utilities (service-area exposure), private wells, and groundwater monitoring sites.
Total Sites
310K
USGS Water Quality Portal
Search Radius
3.1 mi
Per-parcel proximity read
Agency
USGS
USGS Water Quality Portal
About This Database
- Formal Name
- Nitrate Monitoring
- Program
- USGS Water Quality Portal
- Maintaining Agency
- USGS
- Sites Tracked
- 310,265
What This Means for Growers
Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems. Unlike heavy metals, nitrate is a naturally occurring compound that becomes a concern at elevated concentrations. The EPA drinking water standard is 10 mg/L — levels above this in irrigation water can affect crop quality and human health.
The USGS Water Quality Portal mixes three sample types: public water-system tests, private-well samples, and groundwater monitoring wells. A hit at a public water sampling point affects every property on that utility's service area; a hit at a groundwater well speaks to the local aquifer and private-well users in that radius. Municipal users check the utility's annual consumer confidence report for exceedances near or above 10 mg/L; private-well users test the water directly. Certain leafy greens (arugula, spinach, lettuce) are natural nitrate accumulators — they concentrate nitrate from soil and water in their leaves.
Crop Risk Assessment
Leafy greens
Arugula, spinach, and lettuce are natural nitrate accumulators — they concentrate nitrate in leaf tissue.
Root crops
Beets and carrots accumulate moderate nitrate levels, particularly when irrigated with high-nitrate water.
Fruiting crops
Tomatoes and peppers have low nitrate accumulation in fruit tissue.
Tree fruits
Negligible nitrate accumulation in tree fruit — not a concern for orchards.
Know Before You Grow — Mitigation Steps
- 1.Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
- 2.Municipal water is treated and safe — nitrate contamination primarily affects private well users.
- 3.In high-nitrate areas, favor fruiting crops over leafy greens to reduce dietary nitrate intake.
- 4.Avoid over-fertilizing with nitrogen — this compounds the problem in areas with existing nitrate issues.
- 5.Deep-rooted perennials and cover crops can help reduce nitrate leaching in garden soils.
Top States for Nitrate
| State | Sites | Density |
|---|---|---|
| California | 28,434 | 0.18 |
| Kansas | 15,878 | 0.19 |
| North Dakota | 15,844 | 0.23 |
| Pennsylvania | 12,484 | 0.28 |
| Minnesota | 12,286 | 0.15 |
| New York | 11,954 | 0.25 |
| Arizona | 11,388 | 0.10 |
| Louisiana | 10,954 | 0.25 |
| Montana | 10,260 | 0.07 |
| Florida | 10,104 | 0.19 |
| Idaho | 9,840 | 0.12 |
| South Dakota | 9,282 | 0.12 |
| Texas | 9,058 | 0.03 |
| New Mexico | 8,470 | 0.07 |
| Iowa | 8,028 | 0.14 |
| New Jersey | 7,574 | 1.03 |
| Washington | 6,892 | 0.10 |
| Wisconsin | 6,746 | 0.12 |
| Missouri | 5,974 | 0.09 |
| Colorado | 5,952 | 0.06 |
Top Counties for Nitrate
| County | State | Sites | Density |
|---|---|---|---|
| San Bernardino | CA | 4,060 | 0.20 |
| Anchorage | AK | 3,498 | 2.05 |
| Suffolk | NY | 3,314 | 3.64 |
| Maricopa | AZ | 3,302 | 0.36 |
| Barnstable | MA | 3,276 | 8.31 |
| Nassau | NY | 3,138 | 11.03 |
| Riverside | CA | 2,618 | 0.36 |
| Kern | CA | 2,606 | 0.32 |
| Fresno | CA | 1,922 | 0.32 |
| Santa Barbara | CA | 1,912 | 0.70 |
| Los Angeles | CA | 1,718 | 0.42 |
| Chester | PA | 1,656 | 2.21 |
| Ada | ID | 1,592 | 1.51 |
| Pima | AZ | 1,588 | 0.17 |
| San Diego | CA | 1,448 | 0.34 |
| Bernalillo | NM | 1,314 | 1.13 |
| Miami-Dade | FL | 1,282 | 0.67 |
| Lancaster | PA | 1,180 | 1.25 |
| Canyon | ID | 1,140 | 1.94 |
| Salt Lake | UT | 1,104 | 1.47 |
Check Your Address for Nitrate
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