Disinfection Byproducts in San Fernando Valley Drinking Water: TTHMs, HAA5, and the EPA Stage 2 Rule

When LADWP and other San Fernando Valley utilities disinfect tap water, a chemical reaction occurs between the disinfectant and naturally occurring organic matter in the source supply. The reaction produces disinfection byproducts, or DBPs. The two classes regulated under the EPA's Stage 2 Disinfectants and Disinfection Byproducts Rule are total trihalomethanes (TTHMs) and haloacetic acids (HAA5). The federal maximum contaminant level (MCL) is 80 micrograms per liter for TTHMs and 60 micrograms per liter for HAA5. These limits apply as a locational running annual average across each utility's distribution system, not as a single-sample cap. SFV utilities blend imported surface water with local groundwater, and LADWP switched from free chlorine to chloramination specifically to reduce TTHM formation. DBP levels trend up in summer across the Valley as water spends more time in warm pipes. Your utility's annual Consumer Confidence Report is the primary source for your specific readings.

Disinfection byproducts occupy a specific place in the SFV water quality picture. They are not industrial pollutants, groundwater contaminants, or infrastructure failures. They are an unavoidable consequence of treating water with any chemical disinfectant: chlorine, chloramine, chlorine dioxide, or ozone each produces a distinct profile of byproducts when it reacts with the organic carbon already present in the source water. The regulatory question is how to minimize that profile while still achieving the public health protection that disinfection provides. The EPA has been working on that tradeoff since the first disinfection byproduct rules in 1979, and the current framework, the Stage 2 DBPR, has been in effect since 2006. Understanding it helps homeowners interpret the CCR tables that utilities are required to publish every year.

How Disinfection Byproducts Form in SFV Tap Water

The organic matter that reacts with disinfectants to form DBPs originates primarily in the source water: decaying plant material, algae, soil humic acids, and fulvic acids that wash into reservoirs and rivers. When LADWP draws from the Los Angeles Aqueduct (Owens Valley snowmelt) versus the Metropolitan Water District (Colorado River and State Water Project supply), the organic content varies. Colorado River supply tends to carry more dissolved organic carbon than Owens Valley aqueduct water, and the blend ratio shifts seasonally. Local SFV groundwater, drawn from the Tujunga and North Hollywood wellfields, adds a third chemical profile.

When chlorine contacts that organic carbon, the primary reaction products are trihalomethanes (chloroform and its bromine-substituted variants) and haloacetic acids. Temperature accelerates the reaction: warm summer water forms DBPs faster than cold winter water, and water that sits longer in distribution pipes has more time to react. This is why utilities typically see their highest TTHM and HAA5 readings in late summer, at the far ends of their distribution networks where water age is greatest. The EPA disinfection byproducts overview covers the formation chemistry in detail.

The switch to chloramination changes the profile significantly. Chloramine reacts more slowly with organic matter, producing far lower concentrations of the four regulated trihalomethanes than free chlorine would at the same residual level. However, chloramine produces its own set of byproducts, primarily haloacetonitriles (like dichloroacetonitrile), haloketones, and N-nitrosodimethylamine (NDMA), most of which are not currently regulated under the Stage 2 DBPR. LADWP uses chloramination across its system, and its CCR reflects the reduced TTHM profile that chloramine produces compared to the free-chlorine era. The trade-off and the unregulated byproduct question are discussed in the EPA Stage 2 DBPR documentation.

What the EPA Stage 2 DBPR Actually Requires

The Stage 2 Disinfectants and Disinfection Byproducts Rule, published in January 2006 and phased in from 2012 onward, replaced the earlier Stage 1 DBPR's system-wide averaging approach with a tighter locational running annual average (LRAA) framework. The MCLs themselves stayed the same (80 mcg/L for TTHM, 60 mcg/L for HAA5), but the compliance method changed in a way that had real consequences for utilities with large distribution systems.

Under Stage 1, a utility could average results across all monitoring sites. A low reading at the treatment plant could offset a high reading at a far-end location. Under Stage 2, compliance is assessed at each individual monitoring location using a running four-quarter average. A single location that consistently shows elevated DBPs cannot be diluted out by better-performing sites. LADWP, as a large surface-water system, was required to complete an Initial Distribution System Evaluation (IDSE) to identify the sites in its network most likely to have elevated TTHM and HAA5, then place its monitoring points there. The full regulatory framework and applicability table are in the EPA Stage 2 DBPR rule summary.

Why LADWP Uses Chloramine Instead of Free Chlorine

LADWP completed its full conversion to chloramine disinfection across the Los Angeles distribution system in the late 1990s and early 2000s, primarily as a strategy to meet the Stage 1 DBPR TTHM limits that would have been difficult to achieve consistently on free chlorine with the system's source water organic content. Chloramine residuals, typically maintained at 1.5 to 2.5 mg/L in the SFV distribution zones, react with organic matter at a much slower rate than equivalent free chlorine residuals. The practical result is TTHM levels that can run two to four times lower than a free chlorine system would produce under otherwise identical conditions.

Chloramine does produce its own unregulated byproducts, notably NDMA (N-nitrosodimethylamine), which California regulates as a notification level under the state's unregulated contaminant framework, and various haloacetonitriles. These are not currently part of the Stage 2 DBPR reporting requirements that appear in the CCR. California's SWRCB has issued guidance on NDMA, and LADWP's CCR sometimes notes NDMA monitoring under supplemental reporting. The broader background on chloramine trade-offs is in the EPA chloramines in drinking water page. For SFV households, the operational implication is that the chloramine-specific guide at our chloramine overview covers the taste, odor, and treatment differences that chloramine produces compared to free chlorine systems.

How to Read Your LADWP or SCV Water CCR for DBP Data

Both LADWP and SCV Water (Santa Clarita) are required to report TTHM and HAA5 results in their annual Consumer Confidence Reports. LADWP publishes its CCR at the LADWP water quality page. SCV Water's CCR is at yourscvwater.com/water-quality. Burbank Water and Power and Glendale Water and Power publish their own CCRs through their respective utility websites.

In the CCR table, TTHM and HAA5 appear in the disinfection byproducts section. The table typically shows a detected range (lowest to highest reading across the monitoring period), the highest detected individual level, the LRAA (the four-quarter locational average used for compliance), and the MCL. Compare the LRAA to the MCL, not the individual highest detected value. An individual sample can exceed the MCL in a given quarter without triggering a violation if the four-quarter average stays below the limit. The compliance number is the LRAA.

SFV utilities that are in compliance will show TTHM LRAAs and HAA5 LRAAs below their respective MCLs at all monitoring locations. The CCR must state whether any violation occurred during the reporting year. If a violation occurred, the CCR is required to include a notice of the violation, a description of potential health effects, and steps the utility is taking to remediate. Historical compliance records for any California water system are also searchable through the State Water Resources Control Board's Safe Drinking Water Information System (SDWIS) database at the California DDW online information portal. LADWP's PWSID is CA1910067; SCV Water's is CA2910024.

Household Treatment That Reduces TTHMs and HAA5 at the Tap

Both TTHM and HAA5 are amenable to removal by activated carbon, which makes them treatable with equipment that many SFV homes already have or are considering for chloramine and taste/odor control.

Whole-house catalytic carbon. A whole-house catalytic carbon tank sized appropriately for the home's flow rate and water volume will remove chloramine residuals, reduce TTHM precursors (dissolved organic carbon) before they can react further in the home's plumbing, and directly adsorb TTHMs already formed in the distribution system. Catalytic carbon is the correct media choice for chloramine removal; standard activated carbon has limited effectiveness on chloramine. The whole-house filtration component guide explains the media selection in detail.

Point-of-use carbon block (NSF/ANSI 53). An under-sink or countertop carbon block filter certified under NSF/ANSI 53 for TTHM reduction provides measurable reduction at the drinking and cooking tap. NSF/ANSI 53 is the certification standard that covers health-based contaminant reduction claims, as distinct from NSF/ANSI 42 (aesthetic/taste claims) and NSF/ANSI 58 (reverse osmosis). When evaluating a filter for DBPs, verify that the product's NSF/ANSI 53 certification specifically lists TTHM reduction in its scope, not just chlorine taste and odor. The NSF certification search tool allows filtering by contaminant category.

Reverse osmosis (NSF/ANSI 58). RO membranes at the kitchen sink remove the full TTHM and HAA5 panel at very high efficiency (greater than 95% for most compounds) alongside the ionic contaminants (lead, chromium-6, nitrate, PFAS, radionuclides) that carbon alone does not address. If a household is already running an RO system for lead or chromium-6 reduction, it is also handling TTHMs and HAA5 at that tap. The RO service page covers the systems we install across the Valley.

What does not reduce TTHMs or HAA5. Standard activated carbon rated only for chlorine taste and odor (NSF/ANSI 42) does not carry a verified TTHM reduction claim. Whole-house sediment filters, UV systems, and water softeners do not remove TTHMs or HAA5. If DBP reduction is the stated goal, verify the specific NSF certification category of the product, not the marketing description.

Frequently Asked Questions

Are TTHM and HAA5 levels in SFV tap water dangerous?

At levels that SFV utilities are required by law to maintain, below the Stage 2 DBPR MCLs of 80 mcg/L for TTHM and 60 mcg/L for HAA5, the EPA considers the water safe for all uses including drinking, cooking, and bathing. The MCLs were set to balance disinfection protection against DBP risk at the population level, as described in the EPA disinfection byproducts overview. Long-term exposure to DBPs above the MCL is associated with increased cancer risk and, at high concentrations, adverse reproductive outcomes according to the EPA's regulatory record. Utilities that exceed the MCL are required to notify customers and take corrective action. SFV utilities in compliance are meeting those risk-management standards. Households that want to reduce DBP exposure further below the MCL can do so cost-effectively with a carbon block filter certified under NSF/ANSI 53 for TTHM reduction.

Why do TTHM levels vary by season in SFV water?

Three factors converge to produce higher TTHM and HAA5 levels in summer months across the San Fernando Valley. First, warmer water temperatures accelerate the reaction between chlorine (or chloramine) and dissolved organic carbon. Second, summer is when LADWP draws more heavily on Metropolitan Water District imported supply, which carries higher dissolved organic carbon than Owens Valley aqueduct water, giving the disinfectant more organic precursor material to react with. Third, higher summer water demand increases the age of water at the far ends of the distribution network, because turnover slows and water sits longer in pipes where formation reactions continue. The EPA Stage 2 DBPR was specifically designed to address this uneven distribution of DBPs across a system by requiring monitoring at the highest-risk locations rather than averaging across the network.

Does chloramine produce fewer disinfection byproducts than free chlorine?

Chloramine produces significantly fewer of the four regulated trihalomethanes than free chlorine does under equivalent disinfection conditions. That is the primary reason LADWP converted to chloramination. However, chloramine is not byproduct-free. It produces different compounds, primarily haloacetonitriles (like dichloroacetonitrile), haloketones, and NDMA, that are not currently regulated under the Stage 2 DBPR but are monitored under EPA's unregulated contaminant monitoring programs and, for NDMA specifically, under California's state-level guidance. The EPA's full list of currently monitored but unregulated contaminants is maintained at the EPA UCMR page. The CCR exchange involves trading a regulated TTHM/HAA5 reduction for less fully characterized unregulated byproducts, a trade-off the EPA determined net-positive for public health in the Stage 2 record.

Do pitcher filters reduce TTHMs or HAA5?

It depends on the certification, not the filter type. Many pitcher filters carry only NSF/ANSI 42 certification (taste, odor, chlorine aesthetics), which does not include health-based TTHM reduction claims. Some pitcher filters and countertop filters do carry NSF/ANSI 53 certification for specific contaminants including TTHM reduction. To verify: look for the NSF/ANSI 53 mark and check that the certification scope specifically names TTHM (not just chlorine or taste and odor). Filters certified only for NSF/ANSI 42 do not have verified TTHM reduction performance. The NSF product search at nsf.org lets you filter by NSF/ANSI 53 and by specific contaminant including trihalomethanes.

Where do I find my utility's actual TTHM and HAA5 readings?

Your utility's annual Consumer Confidence Report is the required public disclosure document. LADWP publishes its CCR at the LADWP water quality page; SCV Water publishes at yourscvwater.com/water-quality. Burbank Water and Power and Glendale Water and Power publish their own CCRs on their utility websites. In the CCR table, look for the "Disinfection Byproducts" section and find the rows labeled TTHM (or "Total Trihalomethanes") and HAA5 (or "Haloacetic Acids"). The compliance number is the LRAA (locational running annual average), not the individual highest detected value. Historical compliance data for any California water system is also available through the SWRCB SDWIS database at the California DDW online portal.

Can a whole-house carbon system address both chloramine and TTHMs at once?

Yes, and this is exactly what a properly sized whole-house catalytic carbon system does in an SFV home. Catalytic carbon removes chloramine residuals before they can continue reacting with organic matter in the home's internal plumbing, which reduces in-home TTHM formation. It also directly adsorbs TTHMs already present in the incoming water. The combination means reduced TTHM exposure at every tap in the home, including the shower, which matters because TTHMs can volatilize from hot water into the air during bathing. Standard activated carbon does not effectively remove chloramine and therefore has limited value for TTHM control in a chloramine-disinfected supply. Our chloramine guide explains why media selection matters for SFV homes, and the whole-house filtration service page covers system sizing for Valley homes.

Last updated: August 10, 2026. Regulatory thresholds are current as of that date. MCLs and compliance frameworks are subject to revision; verify current DBP standards at the EPA Stage 2 DBPR page and the EPA National Primary Drinking Water Regulations. For utility-specific TTHM and HAA5 data, consult your utility's most recently published Consumer Confidence Report or the California DDW SDWIS database.

Related reading: Chloramine in SFV Water · Gross Alpha Radioactivity in SFV Water · Nitrate in SFV Drinking Water · Arsenic in SFV Drinking Water · Chromium-6 in SFV Water · PFAS in SFV and Santa Clarita · Lead in SFV Water · TCE, PCE, and 1,4-Dioxane in SFV Groundwater · SFV Utility Water Quality Comparison · CA Water Quality Rules 2026 · How Whole-House Filtration Works · What 2,000 SFV Installs Taught Us · Whole-House Filtration · Reverse Osmosis · Water Testing · SFV Water Quality Overview · Service Areas · FAQ · Contact