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Official EPA SDWIS Verified ReportWater Quality & Testing GuideHistorical Record: No Recorded SDWIS Violations

ZIP Code 99176 Water Quality & Testing Report

Thornton, WA · Whitman County County · Updated for 2026

Sahajul HaqueCompiled & verified by Sahajul Haque from official EPA SDWIS records
Public Health & Medical Notice: Drinking water quality data on this page reflects historical compliance records submitted under the Safe Drinking Water Act. This information does not constitute medical advice or a real-time safety guarantee. If you are pregnant, nursing, preparing infant formula, or immunocompromised, consult a healthcare provider. Boiling water kills biological pathogens, but does NOT remove chemical contaminants like lead, arsenic, or PFAS.
Quick EPA Verified Answer

Is Tap Water Safe to Drink in ZIP 99176 (Thornton, WA)?

Caution / Filtration Recommended: Tap water in ZIP code 99176 (Thornton, WA) has compliance concerns, earning an EPA Safety Grade of D (53/100) due to 0 health violation(s) and 0 ppb lead. While treated by ROSALIA TOWN OF, residents are advised to use an NSF/ANSI 53 certified water filter for drinking and cooking.

Safety Score
D

Water Safety Grade

Poor — Multiple violations recorded

Health Violations

0

Total Violations

0

Lead Risk

High

Contaminants

0

About Tap Water in ZIP Code 99176

Tap water in ZIP code 99176 (Thornton, WA) is distributed by ROSALIA TOWN OF (EPA ID: WA5374250), serving approximately 831 residents. Based on EPA Safe Drinking Water Act compliance records, this system receives a water safety grade of D with a composite quality score of 53/100.

Water System

ROSALIA TOWN OF

EPA ID: WA5374250

Water Source

Ground Water

Population Served

831 residents

County

Whitman County County, Washington

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Lead Levels in ZIP 99176

EPA action level: 15 ppb | Public health goal: 0 ppb

Lead Data Not Available

Lead testing data was not found in EPA records for ZIP code 99176. Contact ROSALIA TOWN OF to request lead testing results.

Lead exposure risk in 99176 is rated High. EPA models estimate a 69% exposure probability based on housing and infrastructure age.

Lead Exposure Risk Rating
High
Lead Exposure Probability

EPA model estimate based on housing age and infrastructure

69%
Note: Lead levels above are the 90th percentile from EPA monitoring — meaning 90% of samples were at or below this level. Even "undetected" tap water lead doesn't account for lead leaching from home plumbing. If your home was built before 1986, individual tap testing is recommended.
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Water Hardness & Mineral Content

Grains per gallon (GPG) & Parts per million (PPM / mg/L)

Classification: Moderately Hard5.2 GPG · 89 mg/L

Water in ZIP 99176 is Moderately Hard (89 mg/L / 5.2 GPG). It contains beneficial natural minerals like calcium and magnesium without causing heavy scale accumulation.

Recommendation: A water softener is optional. Regular maintenance of hot water appliances is recommended.
Hardness (GPG)

Grains per gallon

5.2 GPG
Hardness (PPM / mg/L)

Parts per million CaCO3

89 mg/L
Appliance Scaling Risk
Low / Moderate

Official EPA SDWIS Database Entry

Utility: ROSALIA TOWN OF · PWSID: WA5374250

Verify on EPA.gov
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Violation History

Past 5 years — EPA SDWIS data

ROSALIA TOWN OF has recorded zero violations in the EPA compliance database over the past 5 years.

Total Violations (5 yr)
0
Health-Based Violations
0
Unresolved Violations
0
Boil Water Advisories
0
Compliance Risk
Unknown
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Contaminants Detected

Contaminants with health-based violations on record

No health-based contaminant violations are on record for ZIP code 99176 under the Safe Drinking Water Act.

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Water Source & Environmental Factors

Ground Water

This system draws water from underground aquifers. Groundwater is naturally filtered through soil and rock, but can still contain naturally occurring minerals like arsenic, radium, or nitrates.

Water Source Type
Ground Water
EPA Radon Zone

Moderate potential

Zone 2
Energy Burden

% of household income spent on energy — indicator of older infrastructure

5.38%

EPA Radon Zone 2 — moderate radon potential. The EPA recommends testing your home regardless of zone designation.

Water Quality Testing in ZIP 99176

Tap Water & Well Testing Recommendations

Residents in ZIP code 99176 served by ROSALIA TOWN OF can test tap water or private well systems to verify water purity. Testing detects hidden contaminants before they impact family health.

Tap Water Testing Steps

  • 1.Conduct a certified lead check if your home was constructed before 1986.
  • 2.Use certified lab testing kits rather than uncalibrated test strips for regulated compliance.
  • 3.Sample water from both your kitchen faucet and water heater to compare line purity.

Private Well Testing Steps

  • •Test for Coliform bacteria and Nitrates annually.
  • •Test for heavy metals, radon, and PFAS every 3 years.
  • •Send samples to a state-certified drinking water laboratory recognized by Washington State Department of Health.
Certified Lab Testing: Always use an EPA-certified drinking water laboratory in WA for formal legal or real estate compliance testing.

🛡 What Should You Do? — ZIP 99176 Recommendations

  • 🚨 Install a certified NSF/ANSI 53 or 58 (reverse osmosis) filter immediately for drinking and cooking
  • 🚨 Do not give unfiltered water to children, pregnant women, or immunocompromised individuals
  • 🚨 Contact ROSALIA TOWN OF to request the current violation status and corrective action plan
  • 🚨 Report concerns to your state environmental agency or call the EPA hotline: 1-800-426-4791
  • 🚨 Consider having your home's tap water independently tested by a certified lab

Recommended Water Treatment Systems:

REQUIRED FOR SAFETY
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NSF 53 Lead Pitcher Filter

Certified to remove lead. Recommended for immediate protection.

Lead Filter Guide →
STRONGLY RECOMMENDED
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NSF 58 Under-Sink RO System

Reverse Osmosis system certified to remove PFAS, heavy metals, and viruses.

RO System Guide →

Frequently Asked Questions — ZIP 99176 Water Quality

Is tap water safe to drink in ZIP code 99176?+
Tap water in 99176 has a below-average safety grade of D due to compliance issues. We recommend using a certified water filter for drinking and cooking.
How do I get my water tested in ZIP 99176 (Thornton, WA)?+
To test water quality in ZIP 99176, you can order a certified drinking water test kit or send water samples to an EPA/NELAP certified laboratory in WA. Certified testing checks for lead, coliform bacteria, nitrates, hardness, and PFAS that standard test strips miss. Contact Washington State Department of Health for a list of certified regional labs.
How hard is the tap water in 99176?+
Tap water in 99176 is classified as Moderately Hard with an estimated mineral hardness of 89 mg/L (5.2 GPG). A water softener is optional. Regular maintenance of hot water appliances is recommended.
Should I test private well water in 99176?+
Yes. Unlike municipal systems, private wells in 99176 are not regulated by the EPA or local utilities. Private well owners should test their water annually for coliform bacteria and nitrates, and every 3 to 5 years for heavy metals (lead, arsenic) and volatile organic compounds.
What is the lead level in 99176 tap water?+
Lead level data is not available in EPA records for 99176. Contact your utility for details.
Is there an active boil water notice in 99176?+
There are currently no active boil water advisories on record for 99176. Water treatment systems are operating within normal parameters.
Who provides tap water to 99176?+
Tap water in ZIP code 99176 is provided by ROSALIA TOWN OF (EPA ID: WA5374250), serving approximately 831 residents.
What water filter should I use in 99176?+
Based on water metrics for 99176, we recommend Lead & Microplastic Filter. Look for certifications such as NSF/ANSI 53 (Lead Reduction), NSF/ANSI 42 (Particulate/Taste).

Data Sources & Methodology

Water quality data for ZIP code 99176 is compiled from the EPA Safe Drinking Water Information System (SDWIS), EPA ECHO enforcement database, UCMR5 unregulated contaminant monitoring, and Consumer Confidence Reports filed by ROSALIA TOWN OF. Safety scores are composite metrics derived from violation history, lead levels, enforcement actions, and infrastructure risk indicators. Data reflects a 5-year monitoring window. Last dataset update: 2024. View EPA source data →