Charleston Water Hardness & Quality Report (2026)

Charleston, South Carolina — the historic Lowcountry city — draws its municipal water supply from the Commissioners of Public Works (CPW) of Charleston, sourcing from the Edisto River via the Edisto River Intake in Colleton County and supplemental treatment from the North Edisto River Intake, combined with treated water delivered through the Tri-County Water Cooperative regional infrastructure serving the greater Charleston area in Charleston County. The Edisto River is one of the longest free-flowing blackwater rivers in North America, draining the South Carolina Coastal Plain above the Fall Line. Water is treated at the Hanahan Water Treatment Plant before distribution throughout the Charleston metro. Water hardness measures 60 mg/L — classified as moderately soft.

Charleston's moderately soft supply reflects the coastal plain geology of the Edisto River watershed in the South Carolina Coastal Plain. The Edisto River drains terrain underlain by Cretaceous and Tertiary coastal plain sediments — primarily calcareous-poor Cretaceous Middendorf Formation sand and clay and Tertiary Barnwell Group and Santee Limestone formations. While the Santee Limestone contributes some dissolved calcium, the dominant Cretaceous and Tertiary sandy, kaolin-rich sediments of the South Carolina Coastal Plain are largely calcium-poor. The river's blackwater character — stained by tannic acids from wetland drainage — suppresses carbonate dissolution, contributing to the moderately soft finished supply.

With hardness at 60 mg/L, Charleston residents experience minimal scale challenges. Faucet aerators and showerheads rarely need descaling, and kettles develop only light mineral deposits. Soap and shampoo lather well. Dishwashers produce clean glassware with light rinse-aid use. Hot water systems remain largely scale-free. CPW of Charleston consistently delivers water meeting all South Carolina DHEC and EPA Safe Drinking Water Act requirements.