A

Activated carbon filter

Also: Carbon filter, GAC filter

A filter using carbon that has been treated to be highly porous, giving each gram a huge internal surface area. Organic compounds, free chlorine, and many taste and odor compounds physically stick to that surface (adsorption). The most common form is granular activated carbon (GAC). Activated carbon is the workhorse media in most under-sink and whole-home filters. It does not soften water, does not remove dissolved minerals like calcium, and is significantly less effective on chloramine than on free chlorine. Used inside reverse-osmosis systems as a pre-filter and post-filter.

B

Backwash

A self-cleaning cycle where water flow is reversed through the filter or softener tank to lift, agitate, and rinse the bed of media. Backwashing flushes accumulated sediment, iron, and channeling out the drain line. On a softener, backwash is the first stage of regeneration. On a backwashing carbon or sediment filter, it runs on a timer, usually overnight, so the home does not lose pressure during the day. The discharge goes to the home drain via a small drain line connected to the control valve.

Berkeley Water and Sewer (BCWS)

Also: BCWS, Berkeley County Water and Sanitation

The county water and sewer authority for unincorporated Berkeley County, South Carolina. BCWS draws from a mix of surface and groundwater sources and uses chloramine as its disinfectant. BCWS service territory includes Foxbank Plantation and large parts of unincorporated Berkeley County. Hardness, treatment, and disinfectant choices differ from neighboring Summerville CPW and Charleston Water System, so the right home filter strategy is utility-specific.

Bypass valve

A manual or built-in valve at the inlet of a softener or filter that lets water route around the equipment instead of through it. Used during service, media replacement, vacation shutdown, or when the homeowner wants raw water at an outdoor spigot. A clean bypass is a non-negotiable feature of a code-compliant install. Most modern softeners include a quarter-turn bypass on the control valve head.

C

Catalytic carbon

A specially processed carbon with an enhanced surface that can break down chloramine, hydrogen sulfide, and certain other compounds that ordinary granular activated carbon struggles to remove. Important in the Charleston Lowcountry because three of the four major utilities (CWS, MPW, BCWS) disinfect with chloramine, not chlorine. Standard GAC reduces chloramine slowly and inefficiently. Catalytic carbon is the right media choice for a chloraminated supply.

Cation and anion

A cation is a positively charged ion (calcium, magnesium, sodium, iron). An anion is a negatively charged ion (chloride, bicarbonate, sulfate). Ion-exchange softeners use a cation resin that holds sodium and swaps it for calcium and magnesium hardness as water passes through. Anion resins are used in some specialized treatment applications (nitrate or tannin reduction) but are not part of a standard residential softener.

Charleston Water System (CWS)

Also: CWS

The municipal utility serving peninsular Charleston, parts of Mount Pleasant, West Ashley, James Island, Daniel Island, and surrounding areas. CWS draws primarily from the Edisto River and the Bushy Park Reservoir. Hardness is approximately 3.4 grains per gallon, classified as moderately soft. CWS uses chloramine as its disinfectant. CWS has identified approximately 6,000 lead service lines, concentrated in peninsular Charleston, and is executing a $120M replacement program with an EPA deadline of 2037.

Chloramine

A disinfectant formed by combining chlorine with ammonia. Chloramine is more stable than free chlorine, persists longer in distribution pipes, and produces fewer regulated disinfection byproducts. Three of the four major Lowcountry utilities (Charleston Water System, Mt. Pleasant Waterworks, and Berkeley Water and Sewer) use chloramine. The trade-off for homeowners: chloramine is harder to filter than free chlorine. Standard granular carbon strips it slowly. Catalytic carbon is the appropriate media when the goal is full chloramine reduction.

Chlorine

Also: Free chlorine

The classic municipal disinfectant. Used by Summerville CPW as its primary disinfectant. Free chlorine is highly reactive, kills pathogens fast, and is comparatively easy for granular activated carbon to remove. Above roughly 0.5 parts per million, most homeowners can taste or smell it, and chlorine reacts with skin oils and cosmetics in ways some households find drying. Note that chlorine and chloramine require different filtration strategies.

CPW $96M PFAS remediation project

Also: Summerville CPW PFAS project, $96M remediation

A regional capital project to add PFAS-removal treatment at the source for water serving Summerville and surrounding utilities. Total project cost is approximately $96 million, of which Summerville Commissioners of Public Works (CPW) is responsible for approximately $43.5 million. The project is on a 2029 to 2031 completion timeline, aligning with the EPA PFAS National Primary Drinking Water Regulation compliance deadline. Until completion, Summerville CPW itself recommends home filtration as an interim layer.

D

Disinfection byproducts (DBPs)

Also: DBPs, TTHMs, HAA9

Compounds formed when a disinfectant (chlorine or chloramine) reacts with organic matter naturally present in source water. The two regulated families on the federal CCR are total trihalomethanes (TTHMs) and haloacetic acids (HAA5 and HAA9). EWG analysis of Summerville CPW data has flagged TTHMs at approximately 168 times the EWG health guideline and HAA9 at approximately 368 times, while remaining within federal MCLs. Activated carbon and reverse osmosis both reduce most DBPs.

Drain saddle

A clamp-on fitting that taps the home drain line to receive the discharge from a softener regeneration or a filter backwash. Required by plumbing code with an air gap between the drain line and the saddle so dirty drain water cannot siphon back into the equipment. A correctly installed drain saddle is one of the small details that separates a code-compliant install from an inspector callback.

H

Hardness (grains per gallon)

Also: gpg, Water hardness

The combined concentration of calcium and magnesium in water, expressed in grains per gallon (gpg) or parts per million (ppm). 1 grain per gallon equals approximately 17.1 ppm. Classifications: 0 to 1 gpg soft, 1 to 3.5 slightly hard, 3.5 to 7 moderately hard, 7 to 10.5 hard, above 10.5 very hard. Summerville CPW averages 5.5 to 7.2 gpg (moderately hard). Charleston Water System averages 3.4 gpg. Mount Pleasant Waterworks runs lime softening and delivers about 1.7 gpg post-treatment.

Hydrogen sulfide

Also: H2S, Sulfur smell, Rotten egg smell

A dissolved gas that produces a distinctive rotten egg smell. Common on private wells in parts of Berkeley and Dorchester counties, much less common on municipal water. Hydrogen sulfide tarnishes silver, blackens copper plumbing fixtures over time, and is a comfort issue more than a regulated health risk at typical residential concentrations. Treatment options include catalytic carbon, oxidation followed by filtration, or aeration. The right approach depends on concentration and on whether iron is also present.

I

Ion-exchange softener

The standard residential water softener. A tank of cation exchange resin holds sodium ions on its surface. As hard water passes through, calcium and magnesium ions swap places with the sodium, and the water leaves the tank softened. When the resin is loaded with hardness, the system runs a regeneration cycle: a brine solution is drawn from the salt tank, flushed through the resin to displace the captured hardness down the drain, and the resin is reloaded with sodium for the next service run.

Iron and manganese

Two dissolved metals frequently encountered together, especially on private wells. Iron above approximately 0.3 ppm produces orange-red staining on porcelain, laundry, and grout. Manganese above approximately 0.05 ppm produces black or brown staining and a metallic taste. Both can foul softener resin if not addressed. Treatment depends on concentration and form: low levels can be pulled by an iron-rated softener, higher levels need an oxidation and filtration stage upstream of the softener.

K

KDF media

Also: Kinetic Degradation Fluxion

A high-purity copper-zinc alloy media used inside cartridges and tanks for chlorine reduction, heavy-metal reduction, and bacteriostatic control. KDF works by a redox reaction (electron transfer) rather than by adsorption, so it complements activated carbon rather than replacing it. Common in shower filters, in pre-filters upstream of softeners, and inside whole-home cartridge stacks. Less effective on chloramine than catalytic carbon.

L

Lead

A metal regulated under the federal Lead and Copper Rule. Lead is rarely present in source water itself. The risk almost always comes from in-home plumbing, lead service lines, or old solder joints. Summerville CPW completed its lead service line inventory and identified zero lead service lines in its system. Charleston Water System identified approximately 6,000 lead service lines, concentrated in peninsular Charleston and the North Charleston Neck corridor, and is executing a $120M replacement program with an EPA deadline of 2037.

M

Mt. Pleasant Waterworks (MPW)

Also: MPW, Mount Pleasant Waterworks

The municipal utility serving the town of Mount Pleasant, South Carolina. MPW operates a lime-softening treatment plant, which means hardness is removed at the plant before water reaches homes. Post-treatment hardness is approximately 1.7 grains per gallon (29 ppm), in the soft range. MPW uses chloramine as its disinfectant. Because hardness is already low, most Mount Pleasant homes do not need a softener; the question is whether to filter chloramine and disinfection byproducts.

N

NSF International

Also: NSF

A non-profit standards organization that develops the NSF/ANSI standards for water treatment products and operates one of the testing programs that certify products against those standards. NSF certification means a third-party laboratory has verified that the product reduces specific contaminants under specified conditions, at the rated flow, with the rated capacity. NSF certification is product-specific and standard-specific. Always verify current listings at info.nsf.org.

NSF/ANSI 42, 53, and 58

Also: NSF/ANSI 42, NSF/ANSI 53, NSF/ANSI 58

Three of the most-cited drinking water treatment standards. NSF/ANSI 42 covers aesthetic effects (taste, odor, free chlorine, particulates). NSF/ANSI 53 covers health effects (lead, VOCs, cysts, certain PFAS, specific metals). NSF/ANSI 58 covers reverse osmosis systems specifically (TDS reduction plus a list of regulated and unregulated contaminants). A product can be certified to one standard and not another. A product certified to NSF/ANSI 42 has not been tested for lead reduction under NSF/ANSI 53.

P

PFAS (perfluoroalkyl substances)

Also: Forever chemicals, PFOA, PFOS, PFUnA, PFDoA

A family of more than 12,000 synthetic compounds with carbon-fluorine bonds that resist breakdown in the environment and the human body, hence the nickname forever chemicals. The April 2024 EPA PFAS National Primary Drinking Water Regulation sets a 4 parts-per-trillion MCL for PFOA and PFOS with a 2029 compliance deadline. EWG testing of Summerville CPW data detected five PFAS compounds above EWG advisories, most notably PFUnA at approximately 1,183 times the EWG advisory and PFDoA at approximately 75 times. Reverse osmosis and certain NSF/ANSI 53 carbon blocks are the residential treatment options with documented PFAS reduction.

A measure of how acidic or alkaline water is on a scale of 0 to 14. 7.0 is neutral. EPA secondary guidance for drinking water is 6.5 to 8.5. Most Lowcountry municipal supplies fall comfortably within that range after treatment. Low-pH water (acidic) can corrode copper pipes, leaving blue-green staining at fixtures. High-pH water (alkaline) tends to taste flat or slightly soapy. Reverse osmosis water is typically slightly acidic; remineralization or alkaline post-filters are added when that matters for taste or for cooking.

Point-of-entry and point-of-use (POE/POU)

Also: POE, POU, Point of entry, Point of use

Two install categories. Point-of-entry (POE) means whole-home, installed where the main water line enters the house, treats every tap, every shower, every appliance. Softeners, whole-home conditioners, and whole-home cartridge stacks are POE. Point-of-use (POU) means installed at a single fixture, usually under the kitchen sink at a dedicated drinking water tap. Reverse osmosis systems are typically POU. Many homes use a layered strategy: POE for hardness and bulk filtration, POU for drinking water polish.

R

Regeneration cycle

Also: Regen, Brine cycle, Salt tank cycle

The recovery sequence a softener runs to recharge its resin. Stages: backwash (reverse flow lifts and rinses the resin bed), brine draw (a saturated salt solution from the salt tank is pulled through the resin to displace captured hardness), slow rinse, fast rinse, and refill (fresh water is metered back into the salt tank to make next cycle's brine). On a metered modern softener, regeneration runs only after a programmed gallons-treated threshold is hit, usually overnight.

Reverse osmosis (RO)

Also: RO, Reverse-osmosis filtration

A point-of-use treatment in which water is pushed through a semi-permeable membrane that lets water molecules pass and rejects most dissolved solids, including sodium, lead, fluoride, nitrate, many PFAS compounds, and most disinfection byproducts. A typical home RO is a 4 to 6 stage system installed under the kitchen sink: sediment pre-filter, carbon pre-filter, the membrane, a holding tank, and one or more post-filters for taste polish or remineralization. RO produces a small amount of reject water during operation and is the most thorough residential drinking-water treatment available.

S

Salt-free conditioner

Also: Template-assisted crystallization, TAC, Salt-free softener (misnomer)

A whole-home device that does not soften water in the strict ion-exchange sense and does not remove calcium or magnesium. Salt-free conditioners typically use template-assisted crystallization (TAC) media to nudge dissolved hardness ions into a microcrystalline form that is less likely to bond to pipes, water heaters, and fixtures. The water still tests hard on a hardness test strip, but scaling behavior is reduced. Pros: no salt, no drain line, no electricity. Cons: does not give the slick feel of softened water and is less effective in very hard water.

Summerville CPW

Also: CPW, Summerville Commissioners of Public Works

The municipal utility serving Summerville and large parts of Dorchester County, including Nexton, Cane Bay Plantation, and Carnes Crossroads. CPW draws primarily from Lake Moultrie via the Edisto River system and uses chlorine as its primary disinfectant. Hardness averages 5.5 to 7.2 grains per gallon (moderately hard). CPW completed its lead service line inventory and identified zero lead service lines in its system. CPW is investing approximately $43.5 million as its share of the $96 million regional PFAS remediation project on track for 2029 to 2031 completion.

T

Total dissolved solids (TDS)

Also: TDS

The combined concentration of all inorganic and small-organic substances dissolved in water, measured in parts per million (ppm) by a small handheld meter. TDS is a useful aggregate signal but not a contaminant identifier on its own: a TDS reading does not tell you whether the dissolved load is harmless minerals, sodium from a softener, or something to be concerned about. Common Lowcountry tap water reads between 100 and 350 ppm. Reverse osmosis water typically reads under 30 ppm.

W

Whole-home water conditioner

A point-of-entry system that improves water quality across the whole house without using salt-based ion exchange. The category includes salt-free TAC conditioners, multi-stage cartridge stacks (sediment plus carbon plus KDF), and proprietary media systems. A conditioner is the right call when hardness is moderate, the homeowner wants to avoid sodium and a drain line, or when the primary goal is chlorine, chloramine, and aesthetic improvement rather than full hardness removal. Not the same thing as a softener.

Whole-home water softener

A point-of-entry ion-exchange system that removes calcium and magnesium hardness and replaces them with sodium. A softener delivers the slick-feel water that prevents scale on water heaters, faucets, and shower glass, and lets soaps and detergents lather correctly. A softener requires a salt tank, a regeneration cycle, and a drain line. A softener is not a filter and does not, on its own, address chlorine, chloramine, PFAS, or disinfection byproducts. Many Lowcountry homes pair a softener with a separate carbon filter and an under-sink reverse osmosis system.

WQA (Water Quality Association)

Also: WQA

A trade association that develops product testing standards and operates a Gold Seal certification program for water treatment equipment. WQA-tested and WQA Gold Seal certified are not identical to NSF certified, but they reference the same NSF/ANSI standards in many cases. Always check the certification scope: which model number, which standard, which contaminants. Verify current listings at wqa.org. WQA is the relevant authority you will see on softener and conditioner literature; NSF is more often cited for RO and drinking-water cartridges.

Water treatment glossary.

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