The tap water provided by the Charleston Water System (CWS) is safe to drink, consistently meeting or surpassing all state and federal water quality standards. CWS is a member of the Partnership for Safe Water, voluntarily treating water beyond regulatory requirements. This assurance applies to the municipal supply, distinct from private well water which requires separate testing.
The Journey of Charleston’s Water: Source and Purification
Charleston’s drinking water originates primarily from two surface water sources: the Bushy Park Reservoir (about 90% of supply) and the Edisto River (about 10%). This blending of sources ensures an abundant water supply, even during periods of drought.
Raw water is transported through deep tunnels to the Hanahan Water Treatment Plant, the largest treatment facility in South Carolina. There, the water undergoes a multi-step purification process to remove impurities and microorganisms. Treatment begins with the addition of aluminum sulfate (alum), which acts as a coagulant to make tiny suspended particles stick together.
This clumping continues in flocculation basins, where the water’s movement is slowed to allow the larger particles, called floc, to grow. Next, the water flows into sedimentation basins, where gravity pulls the heavy floc particles to the bottom for removal. The partially clarified water then moves through large filters composed of sand, gravel, and anthracite, which capture any remaining microscopic particles.
The final step is disinfection, treating the water with chlorine dioxide and chloramines (a combination of chlorine and ammonia) to protect against pathogens. Chloramines are used because they are stable and maintain a consistent disinfectant residual throughout the distribution system. Fluoride is also added to support dental health before the finished product is pumped out to customers.
Mandatory Testing, Compliance, and Public Reporting
Charleston’s water safety is guaranteed through a rigorous regulatory structure enforced by federal and state agencies. The U.S. Environmental Protection Agency (EPA) establishes national health standards under the Safe Drinking Water Act (SDWA). The South Carolina Department of Health and Environmental Control (SCDHEC) oversees public water systems to ensure compliance with these EPA standards.
The CWS laboratory performs thousands of water analyses each month, continually testing the water during and after treatment. This testing monitors for a wide range of contaminants, including microbiological organisms, industrial chemicals, and heavy metals such as arsenic and atrazine. The results confirm that the water leaving the treatment plant meets or exceeds all established maximum contaminant levels.
Public water systems must publish an annual Consumer Confidence Report (CCR), detailing the previous year’s water quality test results, source water information, and regulatory compliance. This report serves as a transparent summary of water quality, made available to customers, typically by July 1st, and is accessible on the utility’s website. Reviewing the CCR provides customers with the exact levels of any detected substances and confirms the system’s overall compliance record.
Localized Risks and Checking Current Water Alerts
While municipal water leaving the Hanahan plant is safe, quality can be compromised after it enters a home’s private plumbing. The primary concern is localized lead exposure, occurring when water contacts lead service lines, solder, or brass fixtures in older homes. CWS prevents this by controlling the water’s pH and adding orthophosphate, which creates a protective coating inside pipes to inhibit lead leaching.
The utility is aware of approximately 6,000 CWS-owned lead service lines, mostly in older sections of Peninsular Charleston and the Neck area of North Charleston. CWS is executing a multi-year plan to replace all identified lead service lines and offers free lead testing kits to concerned customers. Running the cold water tap for a minute or two before drinking can flush out water that has been sitting in household plumbing.
Temporary safety issues, such as a localized main break or pressure loss, can necessitate a precautionary boil water advisory for a specific area. These alerts are temporary measures issued to protect public health while the utility confirms the water system is free of contamination. Customers should check the Charleston Water System’s official website or social media channels for the most current updates regarding any active boil water advisories or service alerts.