Disinfection Byproducts in Coastal SC Tap Water: What the 2024 Data Shows for BJWSA and Grand Strand Customers

Where do disinfection byproducts come from?

Coastal South Carolina rivers and reservoirs carry high loads of dissolved natural organic matter (NOM): tannins from pine forests, humic acids from tidal marshes, and decomposed plant material that washes in from the region’s extensive wetlands. You can see this NOM in the tea-colored water of the Savannah River, the Waccamaw, and the PeeDee. It is not a pollutant in the conventional sense, but it becomes a problem the moment a treatment plant adds chlorine or chloramines.

When chlorine reacts with NOM, it forms a wide range of chlorinated and brominated organic compounds. The EPA groups the most studied ones into two regulated families. The first is trihalomethanes (TTHMs), which includes chloroform, bromodichloromethane, dibromochloromethane, and bromoform. The second is haloacetic acids (HAA5s), which includes five specific chlorinated and brominated acetic acid variants. Both families form continuously as treated water moves through the distribution system, which means levels rise with water age and peak in summer when warm temperatures accelerate the reaction (U.S. EPA, Stage 2 Disinfectants and Disinfection Byproducts Rule, epa.gov).

The EPA sets the maximum contaminant level (MCL) for TTHMs at 80 micrograms per liter (mcg/L, equivalent to ppb) and for HAA5s at 60 ppb, measured as locational running annual averages (LRAA) under the Stage 2 rule. These are the numbers that appear in your utility’s Consumer Confidence Report. An LRAA is a rolling average of the last four quarters of monitoring at each compliance site, which means a single high quarterly sample does not automatically trigger a violation, but it does raise the average that regulators watch.

It is worth understanding that the EPA’s MCLs were last updated in 2006 and reflect the limits that were technically and economically feasible at that time. The Environmental Working Group (EWG) maintains its own health guidelines based on more recent cancer risk assessments, setting a health goal of 0.15 ppb for total TTHMs (EWG tap water database). That figure reflects a different risk framework than the federal MCL and is not a regulatory limit, but it illustrates why many researchers and public health advocates consider the current federal thresholds to be conservative floor values rather than optimal targets.

For a broader look at how chlorine and chloramines behave in tap water, including the difference between the two disinfectant types, see our dedicated guide.

How we compiled this comparison

This report pulls from three primary sources. First, BJWSA’s 2025 Consumer Confidence Report (covering 2024 test data), which was cited in detail in a Bluffton Sun investigation published August 2025 (blufftonsun.com). Second, the 2026 North Myrtle Beach Water Quality Report (covering 2025 data and the GSWSA-supplied distribution system), analyzed by MyrtleBeachSC News in June 2026 (myrtlebeachsc.com). Third, the EWG Tap Water Database, which compiles state-reported utility testing data for the GSWSA main system (PWS ID SC2620004) and includes individual TTHM component measurements (EWG.org).

Note on scope: this comparison covers BJWSA (serving Bluffton, Hilton Head Island, Beaufort, Port Royal, and Hardeeville) and the GSWSA main surface-water system (serving Myrtle Beach, North Myrtle Beach, Surfside Beach, Conway, Pawleys Island, and Georgetown). It does not cover Charleston Water System, Mount Pleasant Waterworks, or private well water, which have distinct sources and treatment profiles. For Charleston-area and Charleston tap water quality, see our dedicated guide.

BJWSA and GSWSA: disinfection byproducts side by side

The table below presents the key DBP figures drawn from the source documents above. All figures are locational running annual averages (LRAA) unless noted. For context, the EPA MCL is the legal ceiling; a utility that reaches this number in a compliance period is in violation and must notify customers.

BJWSA’s 52 ppb TTHM LRAA represents 65 percent of the federal MCL. At the system level that is compliant, but it also means that some individual distribution zones within the BJWSA network will have higher quarterly readings. The HAA5 picture is more notable: individual monitoring locations reached 73 ppb in 2024, which is 12 ppb above the MCL ceiling. The LRAA for HAA5 was 39 ppb, well under 60 ppb, so no violation occurred. The range, however, illustrates that compliance averages can mask meaningful variation across a large distribution system.

GSWSA’s lower TTHM average reflects two factors. First, GSWSA uses chloramines as its primary disinfectant residual, which produce lower TTHM formation rates than free chlorine. Second, the Grand Strand’s distribution topology may create different water age patterns than the extended BJWSA network, which spans from coastal Hilton Head Island to inland Jasper County communities. For a detailed look at the Grand Strand water quality and GSWSA source water, see our dedicated article.

BJWSA also uses chloramines rather than free chlorine as the residual disinfectant, which already reduces TTHM formation compared to older free-chlorine systems. The 52 ppb LRAA therefore reflects a system that has already made the switch to a lower-DBP disinfection strategy, yet still produces meaningful TTHM and HAA5 concentrations due to the high NOM load in Savannah River source water. For more on the Bluffton-area water profile and whole-house filtration options for BJWSA customers, see our guide to Bluffton water quality and BJWSA whole-house filtration.

What does 52 ppb TTHM actually mean for your body?

Regulatory limits are built on risk assessments that assume a lifetime of daily exposure at the MCL and calculate an acceptable cancer risk increment, typically one additional case per 10,000 or 100,000 people over 70 years of lifetime consumption. Living at 65 percent of the MCL does not mean you absorb 65 percent of the theoretical risk ceiling; the relationship is more complex and depends on which specific TTHM compounds are present, individual metabolism, and total exposure including showering and bathing, not only drinking.

The National Toxicology Program lists chloroform, the largest individual TTHM component in most surface-water systems, as reasonably anticipated to be a human carcinogen (NTP 15th Report on Carcinogens, ntp.niehs.nih.gov). For GSWSA, EWG data shows chloroform alone at 24.9 ppb. BJWSA uses chloramines, which shifts the TTHM profile toward more brominated compounds; those tend to have higher molar potency in some animal studies, though the epidemiological evidence in humans is mixed.

Inhalation and dermal absorption during hot showers add to total DBP exposure. A 2006 study in the journal Environmental Health Perspectives found that shower and bath exposure to TTHMs can rival or exceed drinking-water exposure for some compounds, particularly chloroform (Xu and Weisel, Environmental Health Perspectives, 2006). This means a whole-house point-of-entry filter that treats all water in the home, not just the drinking tap, provides broader coverage than an under-sink or refrigerator filter alone.

It is also worth noting that the BJWSA HAA5 readings at certain locations reached 73 ppb, 13 ppb above the EPA MCL on a single-location basis (though the LRAA remained compliant at 39 ppb). People who live in a part of the BJWSA distribution system that consistently sees higher water age, such as a cul-de-sac at the end of a main or a neighborhood far from a booster station, may experience DBP concentrations above what the system-wide LRAA reports. If you live in Bluffton, Beaufort, or Hilton Head and want to know your specific tap’s DBP level rather than the system average, an in-home water test is the only way to find out. See our guide to choosing the right water treatment system to understand how testing results connect to treatment recommendations.

Which water treatment systems remove disinfection byproducts?

Two certified technologies reduce DBP exposure at home. They are not mutually exclusive: many households combine both.

Activated carbon and catalytic carbon whole-house systems

Activated carbon adsorbs trihalomethanes and haloacetic acids from water as it passes through a carbon bed. NSF International certifies point-of-entry activated carbon systems to NSF/ANSI Standard 58 and 42 for reduction of specific contaminants including TTHMs. For BJWSA customers, where chloramines are the disinfectant, standard activated carbon is less effective at removing the chloramine residual itself. Catalytic carbon, which is granular activated carbon that has been modified to catalyze the breakdown of chloramines, is the more effective choice. Both types remove TTHMs and HAA5s from the water stream.

A whole-house catalytic carbon system treats every water outlet in the home, including showers. This matters because, as noted above, inhalation and dermal exposure during showering contributes meaningfully to total TTHM body burden. Under-counter filters treat only the drinking tap and do not reduce shower or bath exposure. For a full walkthrough of the whole-house filtration installation process on the SC coast, including what to expect on installation day, see our dedicated guide.

Reverse osmosis at the drinking tap

A reverse osmosis drinking water system forces water through a semipermeable membrane that rejects a wide range of contaminants, including TTHMs, HAA5s, PFAS, nitrates, and dissolved salts. RO systems are typically installed under the kitchen sink and treat drinking and cooking water only, not shower water. They are certified under NSF/ANSI Standard 58 for contaminant reduction. RO filtration is compatible with BJWSA and GSWSA water chemistry, though BJWSA’s chloramine residual requires an activated carbon pre-filter to protect the RO membrane from chloramine-induced degradation.

For households concerned about PFAS in South Carolina drinking water in addition to DBPs, an RO system addresses both contaminant categories with a single unit. GSWSA has disclosed PFAS presence in its source water and has active litigation against upstream industrial contributors, making a multi-contaminant approach relevant for Grand Strand customers.

Context: how coastal SC compares to national DBP averages

The EWG Tap Water Database records chloroform (one TTHM component) at 24.9 ppb for the GSWSA system, compared to a national average of 16.2 ppb and a South Carolina state average of 17.4 ppb. This places the Grand Strand system above both state and national benchmarks for that specific compound. BJWSA’s chloramine-based treatment shifts the TTHM mix, producing lower chloroform but more brominated TTHM species; direct comparison to chloroform benchmarks alone does not capture the full picture.

The elevated organic matter in coastal SC source waters relative to inland utility sources is a persistent structural factor. Utilities serving communities built on the SC Piedmont or drawing from groundwater rather than surface water typically show lower DBP levels, because groundwater contains far less dissolved NOM and requires lighter disinfectant doses. For homeowners considering a move or already in the region, this means that DBP management is a routine part of water quality in the coastal plain, not an anomaly. Understanding what your utility reports and adding certified home filtration where appropriate is the practical response.

The environmental impact of water treatment chemicals is also worth noting. Whole-house carbon filtration reduces the chemical load residents are exposed to without introducing additional waste streams. Our article on the environmental impact of water treatment systems covers how to weigh the full lifecycle of different treatment options.

What coastal SC homeowners should do next

The most practical first step is to read your own utility’s current Consumer Confidence Report. Both BJWSA and GSWSA publish these annually and make them available on their websites. BJWSA’s CCR is at bjwsa.org and GSWSA’s is at gswsa.com. Look for the TTHM and HAA5 rows in the regulated contaminants table. The reported level is a system-wide LRAA; your address may be higher or lower depending on where you sit in the distribution network.

If you want your specific tap reading, an in-home water test is the next step. Solomon Home Water Solutions provides free in-home water testing across our service area, which covers Charleston, Bluffton, Hilton Head, Myrtle Beach, and the communities in between. A test takes about 30 minutes and gives you measured results at your tap for TTHM, hardness, iron, pH, and other parameters that matter for sizing the right treatment system.

If your test results show TTHM or HAA5 levels you want to reduce, the treatment path is well established. A catalytic carbon whole-house system addresses DBPs at every outlet, including showers. Adding an RO unit under the kitchen sink provides additional reduction for drinking and cooking water and addresses PFAS at the same time. Solomon installs and services both system types across the coastal SC region. See how the water filtration installation process works in Charleston and surrounding areas.

For homeowners on private well water rather than municipal supply, the DBP question is different. Well water is not chlorinated by the utility, so TTHMs are not a source-water issue. However, if you use a point-of-use chlorine tablet or a whole-house shock chlorination system, DBP formation is possible. Your well water quality report should be checked for nitrates, bacteria, iron, and coliform rather than TTHMs. See our guide to well water versus city water in South Carolina for a comparison of the two supply types and their distinct contaminant profiles.

Summary: key takeaways for BJWSA and GSWSA customers

• Both BJWSA and GSWSA meet all federal Safe Drinking Water Act standards for disinfection byproducts.
• BJWSA’s 2024 TTHM LRAA was 52 ppb (65 percent of the 80 ppb MCL), and HAA5 averaged 39 ppb with some locations reaching 73 ppb.
• GSWSA’s TTHM compliance averages were around 31 ppb for the North Myrtle Beach distribution area.
• Coastal SC surface-water systems tend to produce higher DBP levels than inland or groundwater utilities due to elevated NOM in source waters.
• Whole-house catalytic carbon filtration and point-of-use reverse osmosis are the certified treatment paths for reducing DBP exposure.
• An in-home water test gives you tap-specific readings, not just system-wide averages. Solomon provides this at no charge across our service area.