Chlorination makes city water safe from bacteria and viruses. But the reaction between chlorine and naturally occurring organic matter in source water creates a family of unintended chemical byproducts: trihalomethanes (TTHMs) and haloacetic acids (HAAs). The EPA regulates TTHMs at 80 parts per billion and haloacetic acids (HAA5) at 60 ppb. Utilities across North Carolina and South Carolina currently comply with those limits. Charlotte Water averages 40.8 ppb for TTHMs per public EPA monitoring data, well below the legal ceiling. Raleigh Water averages 21.7 ppb, below the NC state average of 37.1 ppb. However, the Environmental Working Group sets an independent health guideline for TTHMs at 0.15 ppb, based on a 1-in-1,000,000 cancer risk level, roughly 270 times below Charlotte's reported average. For homeowners who want to understand this gap and reduce exposure, here is what the research shows, where NC and SC utilities stand, and what filtration options actually work.
If you want to know your home's specific DBP levels at the tap, schedule a free water test with Aquafeel Solutions across Raleigh, Charlotte, Greensboro, Greenville SC, and 19 NC and SC service communities.
What Are Disinfection Byproducts and How Do They Form?
Disinfection byproducts are chemicals that form when disinfectants, primarily chlorine and chloramines, react with naturally occurring organic and inorganic compounds in raw source water. The organic matter in question is mostly dissolved carbon from decaying leaves, algae, and vegetation. It is naturally present in every river and reservoir used for drinking water supply.
The main regulated DBP families are:
- Trihalomethanes (TTHMs): Chloroform is the most common. When chlorine reacts with organic matter, it produces four THM compounds: chloroform, bromodichloromethane, dibromochloromethane, and bromoform. The EPA regulates the sum of all four as Total Trihalomethanes at a maximum contaminant level (MCL) of 80 parts per billion.
- Haloacetic acids (HAAs): A second class of chlorination byproducts. EPA regulates HAA5 (five specific haloacetic acid compounds) at an MCL of 60 ppb. HAA9 (nine compounds) is used in some monitoring contexts and includes additional members of the same chemical family.
The EPA set these limits under the Disinfectants and Disinfection Byproducts Rules (D/DBPR Stage 1 and Stage 2), finalized in 1998 and 2006. The Stage 2 DBPR required utilities to test at locations most likely to show elevated DBP levels, targeting distribution hotspots rather than masking them in system-wide averages. Current MCLs are listed in the EPA National Primary Drinking Water Regulations table (EPA.gov).
For context on other regulated contaminants in NC and SC water: our GenX and PFAS in NC guide covers industrial PFAS contamination, a different class of chemicals entirely. Our 1,4-dioxane in Pittsboro and the Haw River covers industrial solvent contamination upstream of several NC water intakes.
How Do Charlotte, Raleigh, Greensboro, and Greenville Compare on DBP Levels?
All four major utilities in Aquafeel's service area meet EPA's legal MCLs for TTHMs and HAA5. Here is where each stands based on public monitoring data:
| Utility | TTHM avg (ppb) | HAA5 avg (ppb) | Disinfectant | EPA TTHM MCL |
|---|---|---|---|---|
| Charlotte Water (NC) | 40.8 | 15.3 | Free chlorine | 80 ppb |
| Raleigh Water (NC) | 21.7 | 15.7 | Ozone + chloramine | 80 ppb |
| NC state average | 37.1 | n/a | Varies by utility | 80 ppb |
| Greensboro Water (NC) | Above EWG guideline | Above EWG guideline | Chloramine | 80 ppb |
| Greenville Water (SC) | Above EWG guideline | Above EWG guideline | Surface water treatment | 80 ppb |
Charlotte and Raleigh figures from WaterCheckup.com Charlotte and WaterCheckup.com Raleigh (2026), aggregating from EPA public monitoring data. NC state average from same source. EWG health guideline for TTHMs: 0.15 ppb. Greensboro and Greenville findings reflect published public monitoring data; consult each utility's Consumer Confidence Report for current numbers.
Charlotte Water uses free chlorine as its primary disinfectant, which produces more TTHMs than chloramine under similar conditions. Raleigh uses ozone treatment combined with chloramine, explaining its lower TTHM profile despite serving a similarly sized metro. Both Greensboro and Greenville report TTHMs and HAAs above EWG health guidelines in their public monitoring data, though both comply with EPA MCLs. Greensboro's Consumer Confidence Report is available at greensboro-nc.gov. Greenville Water's 2025 CCR is available at greenvillewater.com.
The EWG guideline of 0.15 ppb for TTHMs is not an EPA regulatory limit. It is based on EWG's risk analysis using a one-in-one-million cancer risk benchmark, which is more conservative than EPA's cost-feasibility-based standard. Our NC municipal water comparison covers additional differences between major NC utility systems.
What Does the Health Research Say About Long-Term TTHM Exposure?
Epidemiological research has associated long-term exposure to elevated TTHM levels in drinking water with increased risk of bladder cancer, colorectal cancer, and adverse reproductive outcomes including miscarriage. The evidence is strongest for bladder cancer. EPA classified chloroform, the most common TTHM, as a "likely human carcinogen" in 2001 based on animal studies. The International Agency for Research on Cancer similarly classified several chlorination byproducts in that range.
Key caveats for interpreting this research:
- These associations reflect long-term exposure, typically decades, at levels more common before the Stage 1 and Stage 2 DBPR regulations tightened utility practices in the late 1990s and 2000s.
- Individual risk from a utility delivering 40 ppb TTHM is small in absolute terms, but it is not equivalent to water containing no DBPs.
- Exposure pathways include ingestion (drinking) and inhalation or dermal contact (showering, bathing). Hot water accelerates THM volatilization, producing measurable inhalation exposure from showers on top of ingestion exposure from drinking.
- The evidence for HAA5 health effects is less extensive than for TTHMs, but HAAs are regulated under the same precautionary approach.
Utilities consistently near the upper allowable range (60 to 80 ppb TTHM) represent a higher-risk profile than utilities like Raleigh Water at 21.7 ppb. For compliance history of any NC or SC utility, the EPA Safe Drinking Water Information System at sdwis.epa.gov is the authoritative federal source.
Private well owners in NC and SC do not face TTHM or HAA exposure from disinfection since private wells are not chemically disinfected by utilities. Well-specific risks are different and are covered in our NC well water testing guide and our hog farm groundwater risks in eastern NC.
Why Do NC Cities Use Chloramines, and Does That Help?
Chloramine is formed by combining chlorine with ammonia in precise ratios. Utilities switched to chloramine starting in the 1990s for one reason: chloramine produces significantly lower TTHM levels than free chlorine under similar conditions. Raleigh, Cary, Apex, OWASA (Chapel Hill and Carrboro), and Greensboro all use chloramines as their primary distributed disinfectant. Charlotte Water uses free chlorine.
The trade-off is not straightforward:
- Lower TTHMs, similar HAAs: Chloramine reduces TTHMs compared to free chlorine but tends to produce different HAA profiles. Some research shows HAA formation can be similar between chloramine and chlorine systems depending on source water chemistry.
- NDMA formation: N-nitrosodimethylamine (NDMA), a probable human carcinogen, forms more readily in chloramine systems than in free-chlorine systems. NDMA is not currently regulated by EPA MCL but is monitored under EPA UCMR programs.
- Nitrification risk in distribution: Chloramine can break down in the distribution system and release free ammonia, feeding bacteria in a process called nitrification. Utilities manage this through residual monitoring, pH adjustment, and targeted flushing programs.
- Compatibility limitations: Chloramine cannot be removed by letting water sit out, as free chlorine can. It requires ascorbic acid or specific dechlorination agents, which matters for aquarium owners and dialysis facilities.
Both chlorine and chloramine systems can produce DBPs well above the EWG health guideline while staying below EPA MCLs. Switching to chloramines reduces TTHMs but does not eliminate the broader DBP picture. See our chlorine vs chloramine guide for Charlotte homeowners and our NC summer water guide for seasonal factors that affect DBP formation throughout the year.
What Raises Disinfection Byproduct Levels at Your Specific Tap?
The utility-reported TTHM average covers the entire distribution system. Your home's actual DBP exposure can be higher or lower than the system average based on several factors:
Position in the distribution system. DBP formation increases as water ages in transit through the system. Homes at the far end of dead-end branches or in low-flow zones tend to receive older water with more accumulated DBP formation time. Homes near treatment plants or pumping stations receive fresher water with lower DBPs but higher disinfectant residual.
Seasonal variation. DBP formation peaks in summer. Warm water accelerates the reaction between disinfectants and organic matter. Source water organic content also tends to be higher after heavy rain events and during algae bloom season. NC and SC utilities typically report their highest TTHM and HAA readings in summer samples, meaning annual averages can understate peak-season exposure at your tap. Our NC summer water quality guide covers seasonal variation and practical steps for warm-weather months.
Hot water use. TTHMs are volatile and off-gas readily from warm or hot water. This produces inhalation exposure during showers and baths on top of ingestion exposure from drinking. HAAs are not volatile and remain dissolved in the water. This means shower DBP exposure is TTHM-dominant while your drinking water exposure includes both compound classes simultaneously.
Water age in your home plumbing. Water that sits in your home's pipes overnight continues producing small amounts of additional DBPs as residual disinfectant reacts with any organic matter on interior pipe surfaces. Running the tap for 30 seconds before filling a glass in the morning reduces this stagnation dose. See our NC water testing cost guide for what a professional tap-point test covers beyond what a utility's annual CCR reports.
What Filtration Options Reduce Disinfection Byproducts in NC and SC City Water?
Not all home filters address TTHMs and HAAs. The type and certification of the filter determines whether it makes a measurable difference for DBPs specifically.
Activated carbon filters certified to NSF/ANSI Standard 53 for VOC and HAA reduction. Carbon is the primary technology for DBP reduction at the point of use. Carbon block filters certified under NSF/ANSI 53 specifically for VOC reduction (covering chloroform and other THMs) and HAA reduction can achieve significant removal. The certification must name these specific contaminants: a general NSF 42 taste-and-odor certification does not cover DBPs and should not be assumed to. Always verify the specific NSF 53 claim before purchasing. Our water filtration cost guide covers carbon filter types and pricing across NC and SC.
Whole-house catalytic carbon filters (point of entry). A whole-house catalytic carbon filter installed at the home's main water entry treats every tap, showerhead, and faucet. This addresses both the drinking water ingestion pathway and the inhalation pathway from showering. Catalytic carbon is more effective than standard granular activated carbon (GAC) for chloramine removal as well as for certain DBP compounds. Our whole-house filtration cost guide for NC covers system types, sizing, and pricing in detail. For Charlotte Water customers on free chlorine, a whole-house catalytic carbon filter eliminates the smell issue covered in our chlorine smell guide and reduces TTHM exposure at every fixture simultaneously.
Reverse osmosis (under-sink, point of use), certified to NSF/ANSI Standard 58. RO membranes remove TTHMs and HAAs alongside PFAS, lead, nitrates, and a broad spectrum of other contaminants. If your water profile includes multiple concerns, such as PFAS (relevant in Raleigh Water's service area, which detected PFOS above the 4 ppt EPA limit in 2026 monitoring data) or lead from older home plumbing, an RO system addresses several contaminant classes together. Our reverse osmosis cost guide for NC covers system selection and what to look for in NSF 58 certification. See our services page for installation options across NC and SC.
What does not effectively reduce TTHMs or HAAs:
- Sediment filters: remove particles and suspended solids, not dissolved chemicals like TTHMs or HAAs.
- Water softeners: remove calcium and magnesium hardness minerals through ion exchange and do not address disinfection byproducts. See our water softener cost guide and our water softener vs conditioner comparison for what softeners do and do not treat.
- Boiling: volatilizes TTHMs into the kitchen air, increasing inhalation exposure while reducing TTHM concentration in the water. HAAs are not volatile and remain in the water as volume reduces, which concentrates them.
Schedule a free in-home water test and we will measure your current DBP profile and recommend the right filter configuration for your home's specific water. Aquafeel Solutions Carolina serves Raleigh, Durham, Charlotte, Greensboro, Winston-Salem, Greenville SC, and 19 NC and SC communities. Book your free water test today.
Disinfection Byproduct FAQs for NC and SC Homeowners
What are the most common disinfection byproducts in NC tap water?
Chloroform is the most prevalent trihalomethane (TTHM) in NC municipal water. Dichloroacetic acid and trichloroacetic acid are the most common HAA5 members. Charlotte Water, using free chlorine, produces more TTHMs than chloramine systems like Raleigh Water. Both utilities comply with EPA limits of 80 ppb for TTHMs and 60 ppb for HAA5.
Is Charlotte tap water safe to drink given its TTHM level?
Charlotte Water meets all EPA regulatory limits, with reported TTHM averages around 40.8 ppb, well below the 80 ppb MCL. Whether that level is acceptable depends on your individual risk tolerance and whether you compare it against the legal standard or the more conservative EWG health guideline of 0.15 ppb.
Do Raleigh's chloramines make its water safer from DBPs than Charlotte's chlorine?
Raleigh Water's average TTHM of 21.7 ppb is lower than Charlotte's 40.8 ppb, partly because chloramines produce fewer TTHMs than free chlorine. But chloramine systems can produce different byproducts including NDMA, and HAA levels can be similar. Neither system is free of disinfection byproducts entirely.
Does a standard pitcher filter remove disinfection byproducts?
It depends on NSF certification. Pitcher filters certified to NSF/ANSI Standard 53 for VOC reduction address TTHMs. Filters certified only to NSF 42 for taste and odor are not certified for TTHM or HAA reduction. Always verify the specific certified claims on your filter, not just the certification number itself.
Does boiling water remove trihalomethanes?
Boiling volatilizes TTHMs into kitchen air, increasing inhalation exposure while reducing TTHM in the water. HAAs are not volatile and remain in the water as volume reduces, concentrating them. For DBP reduction, activated carbon certified to NSF 53 or reverse osmosis certified to NSF 58 is more effective and appropriate.
