Nitrate In Drinking Water In Washington
What residents of Washington need to know about nitrate in drinking water — including how it enters water, which utilities have documented violations, and what steps to take.
Source: EPA SDWIS, Washington State Department of Health (WSDOH), CDC · Last reviewed: 2025-01-01
Quick Answer
Is nitrate in drinking water a real concern in Washington?
Yes — eastern Washington's Columbia Plateau aquifer has documented nitrate issues from intensive irrigated agriculture, and the Yakima Valley has recognized groundwater nitrate concerns.
Is this mostly a public-water issue, a private-well issue, or both?
Primarily private well users in eastern Washington's agricultural regions; some small public water systems in the Yakima Valley and Columbia Basin also have documented nitrate concerns.
What is the main reason residents should care?
Eastern Washington's Columbia Plateau aquifer receives nitrate from irrigated agriculture (dairy, potatoes, hops, wheat, and other crops). Washington's Department of Ecology has documented nitrate hotspots in the Yakima Valley and Columbia Basin.
Key Facts
| EPA Nitrate MCL | 10 mg/L as N |
| Columbia Plateau aquifer | Receives nitrate from irrigated agriculture in eastern WA |
| Documented hotspots | Yakima Valley and Columbia Basin — documented by WA Ecology |
| Agricultural sources | Dairy, potatoes, hops, and grain farming with intensive irrigation and fertilizer use |
| State oversight | Washington State Department of Health (WSDOH) |
Why This Matters in Washington
Eastern Washington, separated from the wet Pacific Coast by the Cascade Mountains, is intensively farmed using irrigation water from the Columbia and Yakima Rivers. Dairy operations, potato farming, hop yards, and grain crops generate significant fertilizer and manure applications. Nitrate leaches from irrigated fields into the Columbia Plateau aquifer, which supplies private wells and some small public systems in Grant, Adams, Franklin, and Yakima Counties. Washington Department of Ecology has documented nitrate hotspots in the Yakima Valley. WSDOH monitors public water systems for nitrate compliance.
Critical — Infants Under 6 Months
Do not use tap water that exceeds 10 mg/L nitrate-nitrogen to prepare infant formula or feed infants under six months. Boiling will concentrate nitrate — do not boil. Use bottled water or a certified reverse osmosis system (NSF/ANSI 58) until the issue is resolved.
Washington Utilities With Nitrate Violation Records
The utilities listed below have at least one nitrate violation on record in EPA's SDWIS database. Violations may be open or resolved — see individual utility pages for current status and risk level.
City of Tacoma Water Division
Tacoma · 446,170 served
City of Vancouver
Vancouver · 373,047 served
City of Bellevue
Bellevue · 321,349 served
City of Everett Public Works Dept.
Everett · 215,774 served
Kent Water Department
Kent · 166,421 served
City of Redmond Water System
Washington · 163,335 served
Clark Public Utilities
Washington · 153,526 served
Lakehaven Water and Sewer District
Washington · 148,809 served
City of Olympia
Washington · 126,966 served
City of Kennewick
Washington · 118,164 served
How Nitrate Gets Into Drinking Water
Agricultural fertilizer and manure runoff
Nitrogen-based fertilizers and animal waste applied to Washington cropland can leach into groundwater or run off into surface water supplies. This is the dominant nitrate pathway in most agricultural regions.
Septic system effluent
Failing or poorly sited septic systems release nitrogen-rich wastewater near drinking water wells. Rural areas with high well density and aging septic infrastructure face elevated risk.
Concentrated animal feeding operations (CAFOs)
Large livestock facilities generate significant waste. Lagoon leaks and overapplication of manure to nearby fields can create localized nitrate hotspots in groundwater.
Natural geological deposits
In some regions, naturally occurring nitrogen compounds in soil and bedrock contribute background nitrate levels to groundwater independent of agricultural activity.
Who Should Pay Closest Attention
Private well users in eastern Washington's agricultural counties — particularly Grant, Adams, Franklin, and Yakima Counties — should test annually for nitrate. Families with formula-fed infants should obtain current test results before using well water.
Households with infants under six months
Pregnant residents
Private well owners in agricultural areas
Households near livestock operations or CAFOs
Rural residents on shallow groundwater wells
Households with older or failing septic systems nearby
How to Check Your Situation in Washington
- 1
Identify your water utility. Use the ZIP lookup below or browse the Washington utility directory on this site.
- 2
Read your utility's page on this site to see its current risk level and any open nitrate violations.
- 3
Review your utility's most recent Consumer Confidence Report (CCR) — mailed annually or available on the utility's website. It must disclose any MCL exceedances.
- 4
If you are on a private well, arrange testing at a Washington State Department of Health (WSDOH)-certified lab. Your state health department maintains a list of certified labs. Annual testing is recommended in agricultural areas.
- 5
If you have an infant under six months, use bottled water or a certified RO system (NSF/ANSI 58) immediately as a precautionary measure — do not wait for test results if you are in a high-risk area.
- 6
If your utility issues a nitrate exceedance notice, follow their guidance and do not use tap water for infants until the issue is resolved.
Treatment Options
Carbon filters and boiling do not remove nitrate. Only the options below are effective.
NSF/ANSI Standard 58 — Reverse Osmosis
RO systems certified to NSF/ANSI 58 reduce nitrate by 85–95% at the point of use. Under-sink installation required. The most practical residential option for nitrate concerns.
Distillation
Distillation units effectively remove nitrate along with most other dissolved contaminants. Suitable for drinking and cooking water — not whole-house use.
Anion Exchange
Ion exchange systems designed for nitrate removal exchange nitrate ions for chloride on a resin bed. Effective as a point-of-entry system; requires periodic regeneration and monitoring.
Carbon filters do NOT remove nitrate
Standard pitcher filters, faucet filters, and under-sink carbon units — including those certified NSF/ANSI 42 or 53 — do not remove nitrate. Do not use these for nitrate reduction.
Frequently Asked Questions
Related Pages
Nitrate — National Overview
All U.S. utilities with nitrate records
Washington State Overview
All utilities and water quality data
Lead in Drinking Water
A separate but common concern
Reverse Osmosis Guide
Removes 85–95% of nitrate
Well Water Guide
Private well testing and safety
All Contaminants
Complete reference library
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
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Washington State Department of Health (WSDOH) ↗