Holtsville Water Hardness & Quality Report (2026)

Holtsville, New York, in Suffolk County — a suburban Suffolk County hamlet in the Town of Brookhaven adjacent to Holbrook and Medford in central Suffolk County, home of the IRS Campus at Holtsville — receives its municipal water from the Suffolk County Water Authority (SCWA), which draws from the Magothy Aquifer (deep Cretaceous coastal plain sand) through SCWA production wells in the Holtsville-Medford-Holbrook corridor of central Suffolk County.

The moderately hard 174.5 mg/L hardness and elevated TDS of 462.1 mg/L are consistent with deep Magothy Aquifer production in central Suffolk County. The Magothy Aquifer (Cretaceous fluvial and deltaic sand and gravel) in the Holtsville-Medford zone is at greater depth than the Upper Glacial zones — longer residence time, greater contact with the Cretaceous marine sediment mineral matrix (iron-silica clay, calcareous shell fragments, glauconite sand), producing the elevated TDS and moderately hard water characteristic of the deep SCWA Magothy production zone in central Suffolk. This matches the North Bellmore Nassau and East Northport Suffolk profiles in this depth zone.

At 174.5 mg/L, Holtsville's water is moderately hard — scale builds in kettles and appliances over months, dishwashers benefit from rinse aid, and faucet aerators need periodic cleaning. Quarterly descaling is appropriate. The PFAS level of 8.3 ppt warrants a certified drinking water filter — the Grumman Bethpage PFAS plume (Nassau-western Suffolk — a documented major PFAS source in the Magothy Aquifer), the Brookhaven National Laboratory (Upton — DOE nuclear facility), and the Long Island defense-aviation PFAS complex contribute to Holtsville's elevated readings.