Public Water Supply 90th Percentiles

This number is calculated from all the lead sample results taken at sites within a water system during a monitoring period. If your water supply’s 90th percentile number is over 12 ppb, your community has a lead Action Level Exceedance (ALE) and must take corrective action.

On January 1, 2025, the lead action level in Michigan was reduced from 15 ppb to 12 ppb. 90th percentiles calculated for samples collected before January 1, 2025 were subject to the 15 ppb lead action level.