ZIP 01821: your water comes from Billerica Water Works
Billerica Water Works is the only community water system that reports serving ZIP 01821 (Middlesex County, Massachusetts) under EPA's UCMR 5 (reported by the system to EPA). PFAS-4 at the latest sample (2025): 5.5 ng/L. Systems report their own ZIP lists to EPA; if your water bill names another utility, that utility's page carries its own results.
Where this ZIP is
This site is a data project, not an official source. If in doubt, check with your water supplier or local authority.