Who serves this area
Most homes in the City of Charleston, including the peninsula and West Ashley, plus Daniel Island, Cainhoy, and nearby communities such as Hanahan and Ladson, receive drinking water from Charleston Water System (CWS), public water system ID SC1010001. CWS is also the retail water provider for James Island and most of North Charleston (see those area pages) and sells treated water wholesale to other utilities, including St. John's Water Company on Johns Island and Mount Pleasant Waterworks.
To confirm your provider, check your water bill or the CWS service area map.
Where the water comes from and how it is treated
CWS has two surface-water sources: Bushy Park Reservoir and the Edisto River. Both are treated at the Hanahan Water Treatment Plant. The utility disinfects with chlorine dioxide and then maintains a chloramine residual in the pipes. It adds orthophosphate and adjusts pH (with lime) so lead and copper are less likely to leach from pipes, and it adjusts fluoride during treatment. CWS is a long-time participant in the Partnership for Safe Water and reports a Phase IV 10-year President's Award for keeping turbidity well below the regulatory requirement.
Sources: CWS 2026 Water Quality Report (2025 data), cover and pp. 4, 6–11, 20–22; CWS water quality page; CWS "What We Do".
How to read these numbers
Utilities must meet a legal limit — usually a Maximum Contaminant Level (MCL), a Maximum Residual Disinfectant Level (MRDL) for disinfectants, or an Action Level (AL) for lead and copper. The health goal, or Maximum Contaminant Level Goal (MCLG), is the level below which EPA expects no known health risk. It is often lower than the legal limit, and it is not a violation if a result is above the health goal but below the legal limit.
PFAS figures below are compared with EPA's current legal limits of 4 parts per trillion (ppt) for PFOA and PFOS, and 10 ppt for PFHxS, PFNA, and HFPO-DA (GenX). Those limits were finalized in 2024. They are not yet being enforced as violations. The original compliance deadline is 2029; EPA has since discussed extending it to 2031. Until a later deadline is finalized, treat 2029 as the date utilities have been told to plan for.
Sources: EPA PFAS drinking water rule; EPA announcement on PFOA and PFOS MCLs; Charleston Water System 2026 Water Quality Report, p. 14.
What's in Charleston Water System water
Figures below are from Charleston Water System's 2026 Water Quality Report, which summarizes calendar year 2025 results (published May 2026). Lead and copper are from the 2024 regulatory sampling round, which the report uses for compliance. Only detected substances that are most useful for a household reader are listed. The utility reported that drinking water met or surpassed all state and federal requirements in 2025.
Source: CWS 2025 data report (PDF) (also at charlestonwater.com/waterreport). Public water system ID SC1010001.
| Substance | Level in CWS water | Legal limit | Health goal (MCLG) | Year | Notes |
|---|---|---|---|---|---|
| Turbidity | Highest 0.09 NTU (range 0.07–0.09); 100% of monthly samples met the limit | Treatment technique: 95% of monthly samples must be under 0.3 NTU | None set | 2025 | Measure of cloudiness; used to check filtration. Report pp. 10–11. |
| Copper (90th percentile at customer taps) | 0.089 ppm (range 0–0.26); no samples over the action level | 1.3 ppm action level | 1.3 ppm | 2024 | Comes mainly from household plumbing. Report pp. 10–11. |
| Lead (90th percentile at customer taps) | 3.5 ppb (range 0–43 ppb); one sample was over the action level | 15 ppb action level (drops to 10 ppb in November 2027) | 0 ppb | 2024 | See the lead section below. Report pp. 10–11, 20–21. |
| Nitrate (as nitrogen) | 0.14 ppm (range 0.14–0.14) | 10 ppm | 10 ppm | 2025 | Report pp. 10–11. |
| Fluoride (finished water) | 0.24 ppm (range 0.07–0.24); 0.16 ppm in source water | 4 ppm | 4 ppm | 2025 | Present in the source and adjusted during treatment. Report pp. 10–11. |
| Chlorine dioxide | Highest 200 ppb (range 0–200) | 800 ppb | — | 2025 | Disinfectant. Report pp. 10–11. |
| Chloramine (running annual average) | 3.0 ppm (range 3.0–3.0) | 4 ppm MRDL | 4 ppm MRDLG | 2025 | Secondary disinfectant in the pipes. Report pp. 10–11. |
| Total trihalomethanes (TTHM) | Locational running annual average 12 ppb (range 2.6–23.9) | 80 ppb | None set | 2025 | Disinfection byproduct. Report pp. 12–13. |
| Haloacetic acids (HAA5) | Locational running annual average 13 ppb (range 4.5–22.4) | 60 ppb | None set | 2025 | Disinfection byproduct. Report pp. 12–13. |
| Chlorite | Highest 0.96 ppm (range 0.37–0.96) | 1 ppm | 0.8 ppm | 2025 | Byproduct when chlorine dioxide is used. Below the legal limit; the highest result was above the health goal. Report pp. 12–13. |
| Total organic carbon | Removal 47% to 61% | Treatment technique (required removal depends on the source water) | — | 2025 | Report pp. 12–13. |
| Total coliform bacteria | Highest monthly share of positive samples: 2.5% (range 0–2.5%); all repeat samples were satisfactory | No more than 5% of monthly samples positive | 0% | 2025 | Report pp. 12–13. |
| Gross alpha (excluding radon and uranium) | 0.376 pCi/L | 15 pCi/L | 0 pCi/L | 2022 | Sampled less often; last results in this report are from 2022. Report pp. 12–13. |
| Selenium | 3.7 ppb | 50 ppb | 50 ppb | 2025 | Report pp. 12–13. |
| Di(2-ethylhexyl) phthalate | 3.7 ppb | 6 ppb | 0 ppb | 2025 | Report pp. 12–13. |
| PFOA (UCMR 5) | Average 4.3 ppt (range 4.1–4.7) | 4 ppt (future standard; not a current violation) | 0 ppt | 2025 | See the PFAS section below. Report p. 14. |
| PFOS (UCMR 5) | Average 5.8 ppt (range 5.2–6.5) | 4 ppt (future standard; not a current violation) | 0 ppt | 2025 | Report p. 14. |
| PFBS (UCMR 5) | Average 3.9 ppt (range 3.7–4.3) | No standalone MCL (used in a future hazard-index standard) | — | 2025 | Report p. 14. |
| PFHxA (UCMR 5) | Average 4.2 ppt (range 3.8–4.6) | No MCL | — | 2025 | Report p. 14. |
| PFPeA (UCMR 5) | Average 4.6 ppt (range 4.4–5.0) | No MCL | — | 2025 | Report p. 14. |
| PFHxS, PFNA, and GenX (HFPO-DA) | Not detected | 10 ppt each (future standards) | — | 2025 | Report p. 14. |
Finished-water characteristics (2025 averages)
These are mostly aesthetic measures (taste, feel, and appearance), not health-based legal limits. Source: same CWS report, p. 22.
| Parameter | 2025 average | EPA secondary guideline (if any) |
|---|---|---|
| Total dissolved solids (TDS) | 100 ppm | 500 ppm |
| Hardness | 54 ppm (3.16 grains per gallon) | No standard |
| Conductivity | 176 µmhos/cm | No standard |
| Sodium | 10 ppm | No standard |
| Alkalinity | 29 ppm | No standard |
| Orthophosphate | 1.1 ppm | No standard (added for corrosion control) |
| Chloride | 15 ppm | 250 ppm |
| pH (monthly finished-water averages) | Year-to-date average 8.7 (range of monthly averages 8.6–9.0) | 6.5–8.5 (secondary guideline) |
pH is from CWS's 2025 monthly finished-water averages, not the annual report table.
Lead
About 6,000 CWS-owned service lines are made of lead. According to CWS, those lines are in the Neck area of North Charleston and Peninsular Charleston, in the corridor between Cosgrove Avenue and The Battery — not typically in West Ashley. Homes built before about 1932 are the most likely to have a lead service line; CWS says it effectively stopped using lead lines in 1932, with records of a small number installed into the 1940s. CWS is replacing lines and cites $34 million in state and federal funds to remove 1,100 of them.
CWS treats water to reduce lead leaching: it has added orthophosphate and controlled pH since October 1992. The utility states there is no lead in treated water leaving the plant, and that no schools in its service area have lead service lines.
The official compliance result in the 2025-data report is from 2024 regulatory sampling: the 90th percentile was 3.5 ppb, below today's 15 ppb action level. One home in that round was above the action level, and the range was 0 to 43 ppb. The same report's chart also lists a more recent July 2025 90th percentile of 2.1 ppb from sampling at homes with lead service lines. The federal action level drops to 10 ppb in November 2027.
Lead still varies from house to house, because it usually comes from a service line, solder, or fixtures — not from the water leaving the plant. CWS offers free lead testing. Call (843) 727-6800, or pick up a kit at a CWS office. You can look up your service line in the CWS inventory map.
Sources: CWS 2026 Water Quality Report, pp. 10–11 and 20–21; CWS lead page.
PFAS
CWS took part in EPA's required UCMR 5 testing. In 2025, average PFOA was 4.3 ppt and average PFOS was 5.8 ppt. Both averages, and the full reported ranges (PFOA 4.1–4.7 ppt; PFOS 5.2–6.5 ppt), sit at or above EPA's future 4 ppt standard. That is not a current violation. Utilities have until at least 2029 to meet the new standard. PFHxS, PFNA, and GenX were not detected in that UCMR 5 set.
CWS has also published voluntary PFAS results since 2018. The April 2025 voluntary results were 5.1 ppt PFOA and 6.3 ppt PFOS — in the same range, from a different sampling date and lab. Results vary from one sampling day to the next.
Source: CWS 2026 Water Quality Report, pp. 14–15.
Disinfection byproducts
CWS uses chloramine in the distribution system and reports relatively low disinfection byproducts: a locational running annual average of 12 ppb TTHM (legal limit 80 ppb) and 13 ppb HAA5 (legal limit 60 ppb) in 2025. The highest individual TTHM result in the reported range was 23.9 ppb. Chlorite, a byproduct of chlorine dioxide, had a highest result of 0.96 ppm, just under the 1 ppm legal limit.
Source: CWS 2026 Water Quality Report, pp. 10–13.
What the utility report can't tell you
A utility report describes water as it leaves the treatment plant and as it moves through the public system. It cannot tell you what comes out of your own faucet.
- Your pipes and fixtures. Lead and copper usually come from a home's service line, solder, or fixtures — especially in homes built before the 1986 federal lead ban — not from the water leaving the plant.
- Private wells. If you are on a well, this report does not apply to you. South Carolina does not regulate private household wells; owners are responsible for testing.
- Older homes. Even when a utility meets every legal limit, a single older home can still have higher lead or copper at the tap.
A useful next step
If you want a snapshot of your own tap water, Auraven Labs offers a free in-home water check. During the visit we measure pH, conductivity, TDS (total dissolved solids), and salinity. Those readings do not detect lead, bacteria, PFAS, or other contaminants, and they do not determine whether your water is safe.
If you want a certified laboratory analysis of your tap water, the City Basic lab test is available for $329.