Washtenaw County, Michigan: drinking water report. Washtenaw County – Ann Arbor and Ypsilanti – serves about 370,000 residents.
Washtenaw County – Ann Arbor and Ypsilanti – serves about 370,000 residents. Ann Arbor draws from the Huron River, while Ypsilanti and other communities purchase from the Detroit-based GLWA system or operate independent groundwater wells. The county's mix of university town, suburban growth, and rural areas creates varied water source profiles.
Ann Arbor's Huron River source has generally provided clean water, though the city has detected 1,4-dioxane – a solvent and likely carcinogen – in its water supply. The contamination originates from a former Gelman Sciences facility, a Superfund site with a groundwater plume that has been migrating toward the city's water supply for decades. Michigan has established a drinking water standard of 7.2 ppb for 1,4-dioxane.
UCMR5 data also shows PFAS detections in county water systems. Michigan's MCLs for seven PFAS compounds apply to all systems. According to the Michigan EGLE's 2024 compliance data, one Washtenaw County system exceeded state PFAS limits and required treatment installation.
Ann Arbor's 1,4-dioxane situation is unique among Michigan cities. The city monitors extensively and treats for the compound, but the contamination plume is still moving.
Check your water for data on both PFAS and 1,4-dioxane in your area. Activated carbon is effective for 1,4-dioxane; reverse osmosis handles a broader range. Our water filter guide covers both. Pull your detailed report, and visit our Michigan page for statewide context.
Drinking water is one exposure route. These federal datasets also cover Washtenaw County, MI.
The EPA places Washtenaw County, MI in Zone 1 - the EPA's highest-risk category, where the predicted average indoor radon level is above 4 pCi/L. Zone maps predict an area's radon potential from geology and existing indoor readings; they say nothing about a specific house. Testing is the only way to know your own level.
54% of homes in Washtenaw County, MI were built before 1980, and 16% before 1950. Residential lead paint was banned in 1978, so housing age is the strongest available proxy for lead-paint exposure. This describes the county's housing stock, not any one home.
Modelled annual fine-particle pollution (PM2.5) in Washtenaw County, MI averages 9.1 µg/m³, above the EPA's annual standard of 9 µg/m³. These are CDC modelled county estimates rather than readings from a specific monitor.
How radon zones work · Air quality by county · Lead exposure guide
28 public water systems serving Washtenaw County, MI have EPA lead testing on record. The reported lead sample skews toward systems that already flagged a problem, so its exceedance rate is not directly comparable with other areas. 5 water systems serving Washtenaw County, MI carry a health-based EPA Safe Drinking Water Act violation.
| Most-cited violation type | Systems affected |
|---|---|
| Lead and Copper Rule Revisions | 2 |
| Revised Total Coliform Rule | 1 |
| Arsenic | 1 |
| Lead and Copper Rule | 1 |
Source: EPA Lead and Copper Rule 90th-percentile tap sampling and EPA SDWIS Safe Drinking Water Act enforcement records, aggregated from the public water systems serving this county. Figures are counts of water systems, not a test of any individual home or tap.