Central Islip Water Hardness & Quality Report (2026)

Central Islip, New York, in Suffolk County — a major central Long Island community (Central Islip is one of the largest communities in central Suffolk County — a diverse Long Island community in the central Long Island residential corridor between Brentwood and Bohemia), home of the former Pilgrim State Psychiatric Center (the largest psychiatric institution in the world at its peak in the 1950s with over 13,000 patients — Pilgrim State's campus in Central Islip is now significantly repurposed as the New York Institute of Technology campus and other uses), a diverse Suffolk County community with a significant Latino-American (particularly Central American Salvadoran and Guatemalan-American) and African-American population, and a major central Long Island residential community — draws its municipal water supply via the Suffolk County Water Authority. Water hardness in Central Islip measures 114.5 mg/L — classified as moderately hard.

Central Islip's moderate hardness reflects the central Long Island glacial aquifer's geology. The Upper Glacial and Magothy Aquifers at Central Islip–central Suffolk County draw from: the Pleistocene Ronkonkoma Terminal Moraine outwash (calcareous-poor Long Island glacial sand — the highly porous, calcareous-poor glacial deposits from the New England granite terrain); the Cretaceous Magothy Formation (calcareous-poor arkosic sand — the primary Long Island deep aquifer). SCWA distribution produces the moderate 114.5 mg/L.

At 114.5 mg/L, Central Islip residents encounter moderate scale accumulation. Monthly cleaning with citric acid solution is recommended. SCWA consistently delivers water meeting all New York State DEC and EPA Safe Drinking Water Act requirements.