Plainfield Water Hardness & Quality Report (2026)

Plainfield, Connecticut, in Northeastern Connecticut Planning Region — a northeast Connecticut town adjacent to Killingly and Griswold in the Quinebaug River Valley of northeast Connecticut — receives its municipal water from the Plainfield Water Division, drawing from local reservoir sources (northeast Connecticut) through the northeast Connecticut water treatment system.

The soft 40.5 mg/L hardness and very low TDS of 74.6 mg/L reflect the northeast Connecticut New England Upland's nearly insoluble crystalline basement — consistent with other northeast Connecticut communities (Killingly: ~38 mg/L; Griswold: ~42 mg/L). The northeast Connecticut watershed drains the New England Upland — Precambrian Hope Valley Alaskite Gneiss (insoluble), Precambrian Waterford Formation gneiss (insoluble), and Permian Narragansett Basin siliceous sedimentary (insoluble). The entirely insoluble New England granite and gneiss basement produces the soft northeast Connecticut supply.

At 40.5 mg/L, Plainfield's water is soft — light scale forms very slowly in appliances, dishwashers are highly efficient, and bathroom fixtures need minimal cleaning. Annual descaling is sufficient. The PFAS level of 6.8 ppt warrants a certified drinking water filter — the Northeastern Connecticut Quinebaug corridor industrial legacy (historic textile manufacturing PFAS), Thames River PFAS background from the Groton-New London submarine base complex, and the Connecticut industrial PFAS legacy contribute to Plainfield's elevated readings.