Charleston floods. It floods during king tides, during hurricanes, during ordinary afternoon thunderstorms. The city sits on a peninsula averaging just 10-12 feet above sea level, and that elevation is shrinking as sea levels rise and the land itself subsides.
For water quality, this means everything. A city that regularly has saltwater in its streets has a fundamentally different relationship with water than one that doesn’t. Charleston’s drinking water story is inseparable from its flooding story.
The Edisto and Bushy Park: Charleston’s Source Water
Charleston Water System (CWS) draws from two primary sources: the Edisto River (via the Edisto River Reservoir) and the Bushy Park Reservoir on the Back River. Together, these surface water sources supply approximately 100,000 customers in the Charleston metro area.
The Edisto River is the longest free-flowing blackwater river in North America — meaning it’s naturally stained dark by tannins leaching from decaying vegetation in its swampy headwaters. This organic loading creates treatment challenges: when chlorine reacts with the high concentrations of natural organic matter, it generates elevated disinfection byproducts (DBPs). Managing trihalomethane and haloacetic acid levels in CWS’s distribution system has been a persistent challenge.
CWS has invested in enhanced treatment, including granular activated carbon and optimized disinfection strategies, to manage DBP formation. But the fundamental chemistry of blackwater source water makes this an ongoing battle rather than a solved problem.
Bushy Park Reservoir provides a somewhat cleaner source but has its own challenges — the Back River is tidally influenced, and saltwater intrusion during drought or very high tides can affect water chemistry at the intake.
Saltwater Intrusion: The Slow Invasion
The Lowcountry’s coastal aquifer systems are under increasing pressure from saltwater intrusion. As groundwater is pumped and sea levels rise, the freshwater-saltwater interface migrates inland and upward, contaminating wells that once produced freshwater.
For CWS’s surface water sources, the concern is different but related: tidal rivers can carry salt upstream during droughts and extreme high tide events. The Bushy Park intake is designed to close during saltwater intrusion events, but the frequency and duration of these events is expected to increase as sea levels continue to rise.
Private wells in the Charleston area, particularly in the barrier islands and the rural communities north of the city, are most vulnerable to saltwater intrusion in the shallow aquifer. The South Carolina Department of Health and Environmental Control (DHEC) monitors chloride levels in coastal wells.
Military PFAS: Joint Base Charleston and Beyond
Joint Base Charleston, which combines the former Charleston Air Force Base and Naval Weapons Station, is a significant PFAS contamination source. Decades of AFFF firefighting foam use at the base’s airfields have resulted in PFAS contamination in groundwater that extends beyond the base perimeter.
The Department of Defense has confirmed PFAS in monitoring wells at Joint Base Charleston at concentrations well above EPA health advisory levels. Remedial investigation is ongoing, and the contamination plume’s interaction with the local aquifer and surface water bodies is being characterized.
Additionally, the former Charleston Naval Shipyard (now the Noisette redevelopment area) has legacy contamination from decades of ship maintenance, including heavy metals, petroleum, PCBs, and potentially PFAS. The site is being redeveloped as a mixed-use community, with environmental remediation proceeding alongside construction.
CWS samples its supply for PFAS, and levels in treated drinking water have been below the EPA’s 2024 MCLs. The city’s reliance on surface water rather than groundwater provides some buffer, but PFAS can enter surface water through contaminated groundwater discharge and stormwater runoff.
Flooding and Water Infrastructure
Charleston’s flooding problem directly affects water quality through several mechanisms:
Stormwater overwhelms the system. During heavy rain — which happens frequently in a city that receives 50+ inches annually — stormwater carries surface contaminants into waterways and overwhelms the combined drainage system.
Saltwater enters the distribution system. When tidal flooding inundates water infrastructure, saltwater can enter the distribution system through air gaps, valve pits, and damaged connections. CWS has had to issue precautionary advisories after extreme flood events.
Sewer system failures. Charleston’s sewer system, much of it over 100 years old, is vulnerable to inflow and infiltration during floods. Sewage overflows into streets, creeks, and the harbor are documented during major rain events. The city has been under consent decree to address these overflows, and billions in infrastructure investment are planned or underway.
What Charleston Residents Can Do
CWS water meets federal standards, but the environmental pressures on the system are real and increasing:
- Review the CCR — Charleston Water System publishes annual reports; pay attention to DBP levels, which can be elevated due to the blackwater source.
- Private well owners on barrier islands or near military installations: test for chloride, PFAS, and general chemistry annually.
- During flood events: follow all boil-water advisories strictly; don’t assume tap water is safe until the utility confirms it.
- Point-of-use carbon filtration can reduce DBPs and improve taste from the tannin-heavy source water.
If you’re concerned about your water quality, a certified water treatment professional can help you test your water and recommend the right solution for your home.