Mount Pleasant, South Carolina
Water Filtration Systems in Mount Pleasant
Its own reverse-osmosis wells tested clean for PFAS. Its purchased Charleston water did not.
Its own reverse-osmosis wells tested clean for PFAS. Its purchased Charleston water did not.
Quick answer: Mount Pleasant Waterworks is unusual: it treats deep aquifer well water through four reverse-osmosis plants and blends it with purchased Charleston water. EPA found all four RO plants non-detect for PFOA and PFOS, while the purchased Charleston water measured PFOS at 6.6 ppt, above the 4.0 limit. Which water reaches your tap depends on where you are. Call (843) 718-8177.
Mount Pleasant is the most interesting water in the metro, and the only one where the answer genuinely depends on which source is feeding your neighbourhood at the time.
The utility pumps from the deep Charleston and Middendorf aquifers and pushes that water through four reverse-osmosis plants. It also buys finished water from Charleston Water System. Those two waters have very different PFAS results.
| Measure | Published figure | Source |
|---|---|---|
| Hardness at the tap | 40–44 ppm · 2.3–2.6 grains | MPW monthly water quality reports · 2026 |
| Source water | Deep aquifer wells through four reverse-osmosis plants, blended with purchased Charleston water | Mount Pleasant Waterworks · 2026 |
| PFOA / PFOS — the four RO well plants | not detected | EPA UCMR5 occurrence data · 2026-08 |
| PFOA / PFOS — purchased Charleston water | 3.6 / 6.6 ppt — PFOS above the 4.0 limit | EPA UCMR5 occurrence data · 2026-08 |
| Total trihalomethanes | 8 ppb against an 80 ppb limit | CWS 2026 Water Quality Report · 2026 |
| Lead, 90th percentile | 1.1 ppb; no lead service lines reported | CWS 2026 Water Quality Report · 2026 |
⚠️ Mount Pleasant Waterworks’ own report appears to label those PFAS figures as coming from RO-treated groundwater. EPA’s raw monitoring data shows they came from the Charleston purchased-water connection, while the RO plants were non-detect in every sample. We publish EPA’s attribution.
Non-detect for both regulated PFAS compounds, in every sample. That is the same technology we recommend under a kitchen sink, operating at municipal scale, and it is a useful demonstration that it works.
Mount Pleasant also buys finished water from Charleston Water System, and that water carries PFOS at 6.6 ppt. Blending varies. If PFAS matters to you, an under-sink unit removes the question entirely.
Tap hardness runs 40 to 44 ppm, about 2.3 to 2.6 grains — softer than Charleston’s and comfortably inside the USGS soft band.
State geological work records a cone of depression around Mount Pleasant with water levels down roughly 200 feet from pre-development, and chloride rising in the Charleston aquifer. The utility has been drilling a deeper test well in response. That is the utility’s problem to solve, not a homeowner’s — but it is the reason the RO plants exist.
Permits in Mount Pleasant go through Town of Mount Pleasant; the licensed plumbing subcontractor pulls it in their own name.
It depends which source is feeding you. All four of Mount Pleasant Waterworks’ reverse-osmosis well plants were non-detect for PFOA and PFOS. The Charleston water it also buys measured PFOS at 6.6 ppt, above the 4.0 limit.
Mount Pleasant’s own report appears to attribute those figures to its RO groundwater; EPA’s raw data attributes them to the purchased-water connection. We follow EPA.
No — 40 to 44 ppm, about 2.3 to 2.6 grains, which is softer than Charleston and well inside the soft band.
Reverse osmosis strips minerals, which is part of why the tap figure is low. A softener has essentially nothing to do here.
Because its deep aquifer water is high in dissolved solids and sodium, and chloride has been rising as saltwater moves inland.
State geological work records water levels down about 200 feet from pre-development around Mount Pleasant. The RO plants make that water potable, and as a side effect they also remove PFAS.