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Tap water quality report

Mercer Island, WA

EPA monitoring detected 15 contaminants across the 2 water suppliers serving Mercer Island. A detection doesn't automatically mean the water is unsafe — see the level at the main supplier for each below, with its EPA source and period.

2
water suppliers
31,153
people served
15
contaminants found
Washington rankings Lead in Washington PFAS in Washington

What was found in Mercer Island's water

The level at the city's main supplier, the highest level anywhere in the city, the EPA limit for each, and where every figure comes from.

ContaminantLevel vs EPA limitSuppliersSource
Nitrate
2100 µg/L 21%
of the EPA limit 10000 µg/L
Highest in the city: SPRING GLEN MOBILE HOME PARK · 96 people · 2019
1/2 SYR4
Nitrate-Nitrite
1984 µg/L 20%
of the EPA limit 10000 µg/L
Highest in the city: SPRING GLEN MOBILE HOME PARK · 96 people · 2019
1/2 SYR4
Copper
180 µg/L 14%
of the EPA limit 1300 µg/L
Highest in the city: SPRING GLEN MOBILE HOME PARK · 96 people · 2017
1/2 SYR4
Total Haloacetic Acids (HAA5)
47.95 µg/L 80%
of the EPA limit 60 µg/L
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
TTHM
47.8045 µg/L 60%
of the EPA limit 80 µg/L
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Chloroform
45.51 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Trichloroacetic Acid
27.255 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Dichloroacetic Acid
21.064999999999998 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Monochloroacetic Acid
3.1910000000000003 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Bromodichloromethane
2.595999999999999 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Arsenic
2.1 µg/L 21%
of the EPA limit 10 µg/L
Highest in the city: SPRING GLEN MOBILE HOME PARK · 96 people · 2017
1/2 SYR4
Lead
1.1 µg/L 7.3%
of the EPA limit 15 µg/L
Highest in the city: SPRING GLEN MOBILE HOME PARK · 96 people · 2017
1/2 SYR4
Dibromochloromethane
0.5500 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Bromoform
0.5000 µg/L
No EPA limit set
Main supplier: MERCER ISLAND CITY OF · 31,057 people · 2019
1/2 SYR4
Lead
0.0063 mg/L 42%
of the EPA limit 0.0150 mg/L
Highest in the city: SPRING GLEN MOBILE HOME PARK · 96 people · 2023
1/2 LCR
Each bar shows the measured level as a share of the EPA limit: green is well under, amber is close to it, red is over. For lead and copper the limit applies to exactly the 90th-percentile figure shown, so red there means a real exceedance. For everything else the limit applies to a running annual average while the figure is the 95th percentile of the system's samples — over 100% is worth reading, but is not by itself a violation. Formal violations are listed separately. These are the utilities' own EPA-reported results, not a city-wide average. A detection means the lab measured the substance — it isn't the same as exceeding a legal limit. Hover a source tag to see the EPA program and years behind each figure.

Water suppliers serving Mercer Island

SupplierPopulation served
MERCER ISLAND CITY OF 31,057
SPRING GLEN MOBILE HOME PARK 96

Frequently asked questions about Mercer Island tap water

Is Mercer Island tap water safe to drink?

EPA testing detected 15 contaminants in the water serving Mercer Island. A detection isn't the same as a violation — most detected levels are within federal limits. Check the level and source for each contaminant above, and your utility's annual Consumer Confidence Report for the official compliance status.

How many water suppliers serve Mercer Island?

2 public water suppliers report drinking-water monitoring for Mercer Island, Washington to the EPA. Each is listed above with its population served.

What contaminants are in Mercer Island's water?

The contaminants EPA monitoring detected in Mercer Island include Nitrate, Nitrate-Nitrite, Copper, Total Haloacetic Acids (HAA5), TTHM. The full list, with the level at the main supplier and the data source, is in the table above.

Where does this data come from?

Every figure is official EPA drinking-water monitoring — the Lead & Copper Rule, the UCMR-5 nationwide testing program, and the EPA Six-Year Review — not our own testing. Each number is labelled with its source and period.