Who serves this area
Johns Island's retail drinking-water provider is St. John's Water Company, Inc. (public water system ID SC1020002), a member-owned cooperative. It is not Charleston Water System, though the water itself is purchased from CWS and treated at CWS's Hanahan plant. St. John's serves nearly 10,000 retail customers in both City of Charleston and Charleston County areas of Johns Island, and it also sells water to Kiawah Island Utilities and the Seabrook Island Water and Sewer Commission.
Sewer on Johns Island, where it exists, may be provided by Charleston Water System or another agency. St. John's provides water only.
Sources: St. John's About Us; St. John's 2025 Annual Water Quality Report (PDF).
Where the water comes from and how it is treated
The source water is Charleston Water System's Bushy Park Reservoir and Edisto River supply, treated at the Hanahan Water Treatment Plant. Treated water reaches Johns Island via crossings near the Stono Bridge, Limehouse Bridge, and the Johns Island Airport. CWS's treatment includes disinfection and corrosion control (orthophosphate and pH adjustment). St. John's then distributes the water and is responsible for sampling in its own system (lead, copper, chloramine, and disinfection byproducts).
Sources: St. John's 2025 Annual Water Quality Report; CWS 2026 Water Quality Report (2025 data).
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 Johns Island water
St. John's reported no violations in 2025 and stated that the water met all federal and state requirements. The first table is from sampling in the St. John's system. The PFAS units in the official St. John's table are printed as ppb; they are converted to parts per trillion (ppt) below (1 ppb = 1,000 ppt) so they can be compared with EPA's 4 ppt standard.
St. John's Water Company system (SC1020002)
| Substance | Level | Legal limit | Health goal (MCLG) | Year | Notes |
|---|---|---|---|---|---|
| Lead (90th percentile at customer taps) | 2.0 ppb (range 0–15); 0 samples over the action level | 15 ppb action level | 0 ppb | 2025 | See the lead section. |
| Copper (90th percentile at customer taps) | 0.057 ppm (range 0.0019–0.081); 0 samples over the action level | 1.3 ppm action level | 1.3 ppm | 2025 | |
| Chloramine residual | 2.6 ppm (range 2.5–2.6) | 4 ppm MRDL | 4 ppm MRDLG | 2025 | |
| Haloacetic acids (HAA5) | 13 ppb (range 8.5–17.8) | 60 ppb | None set | 2025 | Highest level detected, as reported. |
| Total trihalomethanes (TTHM) | 12 ppb (range 6.5–17.3) | 80 ppb | None set | 2025 | Highest level detected, as reported. |
| PFOA (UCMR 5, St. John's) | Average 4.84 ppt (range 4.2–5.4) | 4 ppt (future standard; not a current violation) | 0 ppt | 2025 | Converted from 0.00484 ppb in the official table. |
| PFOS (UCMR 5, St. John's) | Average 6.76 ppt (range 5.0–8.5) | 4 ppt (future standard; not a current violation) | 0 ppt | 2025 | Converted from 0.00676 ppb. |
| PFBS (UCMR 5, St. John's) | Average 4.12 ppt (range 3.6–4.5) | No standalone MCL | — | 2025 | Converted from 0.00412 ppb. |
| PFHxA (UCMR 5, St. John's) | Average 4.38 ppt (range 4.1–4.9) | No MCL | — | 2025 | Converted from 0.00438 ppb. |
| PFPeA (UCMR 5, St. John's) | Average 4.96 ppt (range 4.4–5.6) | No MCL | — | 2025 | Converted from 0.00496 ppb. |
Charleston Water System finished water (as reported by St. John's)
These CWS results are as printed in the St. John's 2025 report and describe the water St. John's purchases. They agree with the CWS 2026 Water Quality Report (2025 data), except that CWS rounds UCMR 5 PFOA and PFOS to 4.3 ppt and 5.8 ppt and lists those results under 2025. St. John's prints 4.325 ppt and 5.825 ppt and labels the sampling window 2023–2025. Turbidity is printed as 0.090 NTU in the St. John's report and 0.09 NTU in the CWS report.
| Substance | Level | Legal limit | Health goal (MCLG) | Year |
|---|---|---|---|---|
| Fluoride | 0.24 ppm (range 0.07–0.24) | 4 ppm | 4 ppm | 2025 |
| Nitrate/nitrite | 0.14 ppm | 10 ppm | 10 ppm | 2025 |
| Sodium | 10.0 ppm | No MCL | — | 2025 |
| Selenium | 3.7 ppb | 50 ppb | 50 ppb | 2025 |
| Gross alpha, excluding radon and uranium | 0.376 pCi/L | 15 pCi/L | 0 pCi/L | 2022 |
| Di(2-ethylhexyl) phthalate | 3.7 ppb | 6 ppb | 0 ppb | 2025 |
| Total coliform (CWS system) | Highest monthly positive share 2.5% | 5% | 0 | 2025 |
| Turbidity (CWS) | Highest 0.090 NTU; 100% of samples met the limit | Treatment technique | — | 2025 |
| PFOA (CWS UCMR 5) | Average 4.325 ppt (range 4.1–4.7) | 4 ppt (future standard; not a current violation) | 0 ppt | 2023–2025 |
| PFOS (CWS UCMR 5) | Average 5.825 ppt (range 5.2–6.5) | 4 ppt (future standard; not a current violation) | 0 ppt | 2023–2025 |
Source: St. John's 2025 Annual Water Quality Report.
Lead
In 2024, St. John's completed a service line inventory. It reported no lead service lines and no galvanized pipe requiring replacement on the company side, the customer side, or the meter-box connections. The utility physically excavated and inspected 1,821 services installed before 1989 (when South Carolina banned lead water pipe) and found none that contained lead pipe or lead parts.
In 2025 tap sampling, the 90th percentile was 2.0 ppb lead (range 0–15 ppb) and 0.057 ppm copper, with no samples over the action level. Lead can still come from fixtures or solder inside a home. For a test, call St. John's at (843) 559-0186.
Source: St. John's 2025 Annual Water Quality Report, lead table and inventory narrative.
PFAS
St. John's 2025 UCMR 5 averages were 4.84 ppt PFOA and 6.76 ppt PFOS, above EPA's future 4 ppt standard. That is not a current violation. The ranges (PFOA 4.2–5.4 ppt; PFOS 5.0–8.5 ppt) are similar to, and in the case of PFOS a little higher than, the CWS finished-water averages St. John's also prints.
Source: St. John's 2025 Annual Water Quality Report, UCMR 5 tables.
Disinfection byproducts
In the St. John's system in 2025, the highest reported TTHM was 12 ppb (limit 80) and the highest reported HAA5 was 13 ppb (limit 60), with ranges of 6.5–17.3 ppb and 8.5–17.8 ppb. Those are well below the legal limits.
Source: St. John's 2025 Annual Water Quality Report, disinfectants and disinfection byproducts table.
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.