Derry Water Hardness & Quality Report (2026)

Derry, New Hampshire, in Rockingham County — a growing southern New Hampshire community along the I-93 and Route 28 corridor, birthplace of astronaut Alan Shepard (first American in space) and the childhood home of poet Robert Frost — receives its municipal water from the Town of Derry Public Works Water Division, which draws from Beaver Lake and the Fordway Brook watershed impoundments in the Rockingham County crystalline upland. Derry's water supply reflects southern New Hampshire's exceptional granite bedrock terrain.

The 18 mg/L hardness and TDS of 28.9 mg/L are among the softest and most mineral-free in this entire dataset — one of the cleanest water supply signatures in the northeastern United States. Beaver Lake and the Fordway Brook watershed drain the Proterozoic Avalonian terrane of southeastern New Hampshire — the Massabesic Granite (Carboniferous biotite granite and related Avalonian igneous bodies), Paleozoic metamorphic rocks, and the relatively thin glacial soils of the Merrimack Lowland. These ancient crystalline rock terrains have extremely low solubility — the granite and gneiss minimize dissolved mineral contributions — and New Hampshire's abundant rainfall (45+ inches/year) over forested, protected reservoir watersheds maintains exceptionally soft, low-TDS source water. Derry's supply exemplifies New England's finest mountain granite water quality.

At 18 mg/L, Derry's water is extremely soft — excellent for all household appliances and plumbing. Scale essentially never forms under normal use. Soap lathers abundantly, the dishwasher performs at peak efficiency, and appliances have maximum mineral-free lifespan. However, very soft water can be mildly aggressive toward plumbing — homes with older copper pipes should flush cold taps briefly before drinking and consider a phosphate corrosion inhibitor. Annual descaling of heating appliances (if any) is purely precautionary. The PFAS level of 3.9 ppt warrants a certified drinking water filter — Derry's location along the I-93 corridor and the Rockingham County southern New Hampshire tech and light industrial zone contribute to a modest PFAS background.