Montgomery County, MD
drinking water quality
1,082,273 residents · 57 public water systems · 48 ZIP codes
EPA sampled 3 of 57 public water systems here, together serving about 1,958,005 people. The highest reading was PFOS at 6.5 ng/L at Town Of Poolesville. 1 of the sampled system was above a federal limit. Last sampled 9/22/2025.
What was found
| Compound | Highest result | Federal limit | Ratio |
|---|---|---|---|
| PFOS | 6.5 ng/L | 4 ng/L | 1.6× |
| PFOA | 5.4 ng/L | 4 ng/L | 1.4× |
| PFHxS | 6.9 ng/L | 10 ng/L | 0.7× |
Also detected, with no federal limit set: lithium (41100 ng/L), PFPeA (15.1 ng/L), PFHxA (9.8 ng/L), PFBA (8.9 ng/L), PFHpA (5.4 ng/L).
Health-based violations
Separately from PFAS, EPA records 14 health-based violations across 9 of the county’s water systems since 2020, the most recent in 2025. They involved E. coli, nitrate, total coliform.
What this means
PFAS are industrial chemicals that EPA describes as breaking down only very slowly in the environment. In April 2024 EPA set the first enforceable national limits: 4 ng/L for PFOA and PFOS, 10 ng/L for PFHxS, PFNA and GenX.
These figures are county-level and come from EPA’s sampling of public water systems. They describe the worst result found in the county, not what comes out of any particular tap — that depends on which system serves the address, and on the plumbing in the building. A private well is not covered by this programme at all.
ZIP codes in Montgomery County
20812 · 20814 · 20815 · 20816 · 20817 · 20818 · 20832 · 20833 · 20837 · 20838 · 20839 · 20841 · 20842 · 20850 · 20851 · 20852 · 20853 · 20854 · 20855 · 20860 · 20861 · 20862 · 20866 · 20868 · 20871 · 20872 · 20874 · 20876 · 20877 · 20878 · 20879 · 20880 · 20882 · 20886 · 20889 · 20892 · 20894 · 20895 · 20896 · 20899 · 20901 · 20902 · 20903 · 20904 · 20905 · 20906 · 20910 · 20912
Readings are county-level, so every ZIP here shares the figure above. Search your ZIP on the map to see it in context.