Largest public system
- Chester Metropolitan District: TTHM (disinfection byproducts)
- 30.5 ppb
- Highest running annual average (2025); federal limit 80 ppb.
- Chester Metropolitan District, 2025
- Chester Metropolitan District: HAA5 (disinfection byproducts)
- 15.2 ppb
- Highest running annual average (2025); federal limit 60 ppb.
- Chester Metropolitan District, 2025
- Chester Metropolitan District: Lead (at sampled homes' taps)
- 0 ppb
- 90th percentile of homes sampled (2022); 1 sampled home above the action level. The federal action level is 15 ppb.
- Chester Metropolitan District, 2025