King County, Washington has about 2,340,211 residents (Census 2024 estimate) and 156 community water systems in EPA records. The largest local system is Seattle Public Utilities, serving about 1,161,961 people from surface water.
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
Seattle Public Utilities Measured (utility report, 2024 (quarterly analysis 2024-02-27)) · High confidence
1.4 gpg (25 mg/L, system (Cedar and Tolt plant outlets and distribution)), soft · range 23.6–25.9 mg/L
Source: SEATTLE PUBLIC UTILITIES water quality report, 2024 (quarterly analysis 2024-02-27)
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
For a 3-person home using 57 gallons per person per day and regenerating weekly, you'd remove about 1,676 grains between regenerations. Suggested size: 24,000 grain.
Estimate only. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
The 6 biggest of 156 community water systems on EPA records for this county. Service areas don't follow county lines; your water bill names your provider.
WA5377050 · serves about 1,161,961 people · Surface water
Lead 90th percentile: 1.6 ppb (period starting 2025-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
WA5305575 · serves about 321,349 people · Surface water
No lead result in this dataset.
WA5338150 · serves about 166,421 people · Surface water
Lead 90th percentile: <DL (below the lab detection/reporting limit; reported as 0) (period starting 2022-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
WA5371650 · serves about 163,335 people · Surface water
Lead 90th percentile: 2 ppb (period starting 2022-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
WA5341997 · serves about 148,809 people · Surface water
Lead 90th percentile: 3.3 ppb (period starting 2023-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
WA5371850 · serves about 108,091 people · Groundwater
Lead 90th percentile: 1.9 ppb (period starting 2023-01-01) Older result. Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
A PFAS detection is not a violation. Federal limits (4 ppt for PFOA and PFOS) apply to running annual averages, with compliance required by 2029. In May 2026 EPA proposed extending the PFOA/PFOS deadline to 2031 and removing other PFAS limits; not final as of 2026-10-21.
These are public records for whole systems. Your home's pipes, fixtures and any private well can change what you drink. A certified lab test or a hardness test strip gives you your own numbers. Then use our PFAS and lead filter selector to see which certifications to look for.
None of the 6 largest systems here have a health-based violation in EPA records since October 2021. Seattle Public Utilities's most recent lead 90th percentile was 1.6 ppb (2025), below the 15 ppb action level. Public records can't guarantee what comes out of your tap, especially with older plumbing, so a home test is the surest check.
Seattle Public Utilities reports about 1.4 grains per gallon (25 mg/L), which is soft. For a 3-person home at 1.4 gpg, our softener calculator suggests a 24,000 grain unit as a starting point.
4 of the 6 sampled systems listed here detected at least one PFAS in EPA's UCMR 5 testing, and 2 results were above the level of a federal limit in at least one sample. A detection isn't a violation: federal PFAS limits apply to running annual averages starting in 2029.
Most homes are served by Seattle Public Utilities or one of the other systems listed on this page, but service areas don't follow county lines. Your water bill names your provider, and its annual Consumer Confidence Report has the full test results.
Data as of October 21, 2026. Figures are copied from public records and combined with our own calculations; they can be out of date or wrong. Tapped Out isn't affiliated with any utility or the EPA. Written and reviewed by the Tapped Out team. How we calculate · All sources.