Derry Water Hardness & Quality Report (2026)

The Derry Water Department serves approximately 17,210–34,000 residents across Derry, New Hampshire, drawing from two primary sources: Beaver Lake (surface water) and groundwater wells. The utility operates under state and federal regulatory oversight and publishes annual Consumer Confidence Reports (CCRs) detailing water quality, treatment protocols, and compliance data. Treatment processes include chlorination and pH adjustment to maintain regulatory compliance. The service area encompasses Derry in Rockingham County, relying on both surface and groundwater sources that are monitored through the utility's ongoing quality assurance programs.

Derry's water supply originates in the Beaver Lake watershed and glacial groundwater aquifers underlying Rockingham County. The underlying geology consists of Precambrian granite, metamorphic bedrock, and glacial deposits characteristic of southern New Hampshire. These formations naturally contribute dissolved minerals — particularly calcium and magnesium — to both surface and groundwater, resulting in a moderately mineralized supply typical of New England's post-glacial aquifer systems.

At its moderately hard classification, Derry's water may cause scale buildup in water heaters, kettles, and appliances over time, though the effect is less severe than in harder-water regions. Residents may notice soap residue on dishes and skin; some prefer point-of-use or whole-home filtration for taste and appliance longevity. A water softener is optional but often recommended for households with sensitive appliances. Derry's tap water meets all EPA Maximum Contaminant Level Goals (MCLGs) with zero MCL violations reported; however, third-party analysis has identified hexavalent chromium, combined radium (radium-226 and radium-228), PFAS, arsenic, chloride, and fluoride at levels above health-advocacy guidelines, though below EPA legal limits. The utility employs standard treatment including chlorination and pH adjustment to maintain federal drinking water compliance.