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.