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TTHM Concentration in New Mexico Community Water Systems: Annual Mean and Maximum TTHM Concentration (Micrograms per Liter) and Year, 1999 to 2022

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Why Is This Important?

Disinfection byproducts (DBP) are formed when disinfectants, such as chlorine are used in a water treatment to inactivate (or kill) pathogens (i.e., disease causing organisms) present in the source of water (i.e., lake, river, reservoir, or ground water aquifer). Different disinfectants produce different types and amounts of DBPs that may be harmful to human health. Therefore, the Environmental Protection Agency (EPA) developed requirements or regulations for water treatment that would both protect people from waterborne pathogens and related diseases and the potential harmful effects of DBPs. Most common DBPs are produced when chlorine reacts with natural organic matter (e.g., decaying vegetation) present in the source water. Water in which DBPs are present is a very complex mixture. Formation and presence of DBPs is dependent on a number of factors, including the chemical disinfectant used, water quality conditions such as the content and amount of organic matter, pH, temperature, disinfection method used, and duration of treatment (how long disinfectant is in contact with the water, which means that if a person lives on the very outer edge of the water distribution system, the person will have higher levels of DBPs in the water than someone right next to the water treatment facility). Other factors include the combination or sequential use of multiple disinfectants or oxidants. Furthermore, the composition of the DBP mixture may change seasonally. The highest levels of DBPs are expected to be formed in water derived from surface sources (such as rivers, lakes, or reservoirs) because ground water usually contains little organic matter. About 500 different chlorination byproducts have been identified, including trihalomethanes (THMs) and haloacetic acids (HAAs), which are the most prevalent byproducts and some of which are carcinogenic to experimental animals. However, none of the individual DBPs dominates the toxicity of this mixture and potential chemically-related toxicity or health effects are a function of exposure to the DBP mixture. Some people who drink water containing TTHMs in excess of EPA's standard and over many years may experience health problems of the liver, kidney, or central nervous system and increased risk of developing some cancers (such as bladder, rectal, and colon cancer), especially cancer of the urinary bladder (; . Some THMs have also been shown to cause adverse reproductive and developmental effects in experimental animal studies (such as reduced sperm motility). Among a few human studies evaluating the association between exposure to DBPs and reproductive and developmental effects or adverse pregnancy/birth outcomes, some suggested an increased risk from exposure to DBPs while others have shown none. Although findings about adverse pregnancy outcomes have not been definitive, DBPs have been implicated in fetal loss and a variety of adverse birth outcomes, including growth retardation and birth defects (e.g., neural tube defects). Note that exposure to THMs in drinking water may also occur by inhalation or skin absorption, in addition to ingestion of contaminated drinking water.


Total trihalomethanes or TTHM concentrations (measured as the sum concentration of chloroform, bromodichloromethane, dibromochloromethane, and bromoform in micrograms of TTHMs per liter of water or mcg/L) in community drinking water systems (CWS) are combined with information about each CWS (such as service population) to generate the following measures shown in this report: 1) statewide TTHM concentration distribution in CWSs by mean and maximum over time, 2) annual distribution of mean and maximum TTHM concentration for persons served by CWS and 3) annual distribution of mean and maximum TTHM concentration by CWS. EPHT data queries -- -- provide detailed results by year for 1) mean TTHM concentration by CWS for a select year, 2) maximum TTHM concentration by CWS for a select year, 3) mean TTHM concentration and the number of CWS by year, 4) maximum TTHM concentration and the number of CWS by year, 5) mean TTHM concentration and the number of persons served by year, 6) maximum TTHM concentration and the number of persons served by year, 7) quarterly distribution of number of CWS by mean TTHM concentration or 8) quarterly distribution by number of people served by mean TTHM concentration. Additionally, users may query the number of persons served and the number of CWS in the state for a select year. A CWS is a public water system (PWS) that serves year-round residents of a community, subdivision, or mobile home park that has at least 15 service connections or an average of at least 25 residents. These CWSs are a subset of all New Mexico PWSs. To measure TTHM concentration in CWS, drinking water samples are usually taken at entry points to the distribution system or representative sampling points after water treatment has occurred. Data Source: New Mexico Environment Department's Drinking Water Bureau, New Mexico Safe Drinking Water Information System (SDWIS). Measured TTHM concentrations in finished drinking water can be used to understand the distribution of potential trihalomethanes (THM) exposure level for populations served by community water supplies. Due to potential errors in estimating service population, the measures may overestimate or underestimate the number of potentially affected people. These measures allow for comparisons of potential THM exposure between the populations served by different water systems over time.

How the Measure is Calculated

  • Numerator:

    Concentration of TTHM.
  • Denominator:

    Not applicable.

Health Topic Pages Related to: Community Water: Total Trihalomethanes (TTHM) Concentration - Disinfection Byproducts

Indicator Data Last Updated On 08/12/2023, Published on 11/02/2023
Environmental Health Epidemiology Bureau, Environmental Public Health Tracking Program, Epidemiology and Response Division, New Mexico Department of Health, 1190 S. Saint Francis Drive, Suite 1300, Santa Fe, NM 87505, Srikanth Paladugu, Bureau Chief,, or Chelsea Langer, Environmental Epidemiologist Supervisor,