A92/100
Mercer Island Tap Water Quality: Is It Safe to Drink? (2026 Report)
Serving 30,689 residents · Washington
What's In Mercer Island's Tap Water?
68
Contaminants Tested
0
Exceed EPA Limits
0
Above EPA Goals
EPA Violation History
No violations in the past 5 years
Full EPA compliance since 1992.
Understanding violation severity
Tier 1Urgent health risk. Utility must notify all customers within 24 hours.Tier 2Important health or treatment issue. Customers notified within 30 days.Tier 3Administrative or monitoring issue. Reported in the annual water quality report.
Source: EPA Safe Drinking Water Information System (SDWIS) · Updated quarterly
Water Utility Details
MERCER ISLAND CITY OF
Population Served
30,689
Water Source
Purchased Surface Water
System ID
WA5353640
Frequently Asked Questions About Mercer Island Water
Is Mercer Island tap water safe to drink?
Mercer Island, Washington tap water receives a grade of A (92/100), which is considered excellent. Out of 68 contaminants tested, none exceed EPA maximum contaminant levels (MCLs). While the water meets federal standards, some residents may still choose to use a filter for additional peace of mind.
What contaminants are in Mercer Island's water?
68 contaminants were tested in Mercer Island's water supply. No contaminants exceed EPA legal limits (MCLs) or health goals (MCLGs), which is a positive indicator of water quality.
Does Mercer Island have any water quality violations?
Yes, Mercer Island has 4 EPA violation(s) on record, with the most recent in 1992. Violation types include MR, MCL. 1 of these are health-based violations, which are the most serious category.
Do I need a water filter in Mercer Island?
Mercer Island water meets EPA standards, so a filter is not strictly necessary. However, some residents prefer the added security of a water filter. EPA health goals (MCLGs) are stricter than legal limits and are set at levels with zero expected health risk. All contaminants are within health goals.
Where does Mercer Island's tap water come from?
Mercer Island's drinking water is sourced from purchased surface water and supplied by MERCER ISLAND CITY OF. The system serves approximately 30,689 people. Surface water sources include rivers, lakes, and reservoirs.
How often is Mercer Island's water tested?
Under the Safe Drinking Water Act (SDWA), water utilities are required to regularly test for over 90 contaminants. Testing frequency varies by contaminant — some are tested monthly, others quarterly or annually. Mercer Island's water systems must report results to the EPA and publish an annual Consumer Confidence Report (CCR). The data on this page reflects the latest available EPA testing data.
How does Mercer Island's water compare to other cities in Washington?
Mercer Island's water quality score of 92/100 earns a grade of A, which is considered excellent. This places Mercer Island among the better-performing water systems in Washington. Visit our Washington state page to see how all cities in the state compare.
What should I do if I'm concerned about Mercer Island's water quality?
If you have concerns about Mercer Island's tap water, consider these steps: (1) Request your utility's annual Consumer Confidence Report for detailed local data. (2) Get your water independently tested through a state-certified laboratory. (3) Consider an NSF-certified water filter rated for the contaminants found in your area. (4) Contact your water utility (MERCER ISLAND CITY OF) with specific questions. (5) Report water quality issues to your state drinking water program or the EPA Safe Drinking Water Hotline at 800-426-4791.