Know Your Environment. Protect Your Health.

Total trihalomethanes (TTHMs)

City of Nampa

Trihalomethanes are cancer-causing contaminants that form during water treatment with chlorine and other disinfectants. The total trihalomethanes group includes four chemicals: chloroform, bromodichloromethane, dibromochloromethane and bromoform. Read More.

Studies conducted in the U.S. and Europe have found that drinking tap water that carries disinfection byproducts increases the risk of developing bladder cancer. In animal studies, all trihalomethanes cause liver, kidney and intestinal tumors. Some human epidemiological studies also reported an association between disinfection byproducts and an increased risk of problems during pregnancy, including spontaneous miscarriage, cardiovascular defects, neural tube defects and low birth weight.

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

Click here to read more about disinfection byproducts.

 

100

Samples

0

Samples exceeding legal limit (MCL)

81

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
20183.18 ppb1613ND - 5.66 ppb
20193.41 ppb2015ND - 8.36 ppb
20204.13 ppb1613ND - 8.17 ppb
20213.79 ppb1613ND - 14.3 ppb
20224.41 ppb1612ND - 13.6 ppb
20234.10 ppb1615ND - 9.70 ppb

ppb = parts per billion

State, National, and Health Guidelines for Drinking Water

EWG Health Guideline: 0.15 ppb

The health guideline of 0.15 parts per billion, or ppb, for the group of four trihalomethanes, or THM4/TTHM, was defined in a peer-reviewed scientific study by EWG and represents a one-in-one-million lifetime cancer risk level.

EPA Maximum Contaminant
Level (MCL): 80 ppb

The legal limit for the group of four trihalomethanes, established in 1998, was based on the need for residual disinfectant levels in water served to customers and the cost of treatment. This limit does not fully protect against the risk of cancer due to exposure to trihalomethanes.

ppb = parts per billion

All test results

Date Lab ID Result
2018-01-10D1801343ND
2018-01-10D18013442.43 ppb
2018-01-10D18013462.94 ppb
2018-01-10D18013452.49 ppb
2018-05-02D18195785.66 ppb
2018-05-02D18195774.48 ppb
2018-05-02D18195764.22 ppb
2018-05-02D18195751.08 ppb
2018-08-13D1839491ND
2018-08-13D18394944.38 ppb
2018-08-13D18394934.74 ppb
2018-08-13D18394924.45 ppb
2018-10-08D1850031ND
2018-10-08D18500344.45 ppb
2018-10-08D18500334.86 ppb
2018-10-08D18500324.63 ppb
2019-01-30D19043393.64 ppb
2019-01-30D19043384.65 ppb
2019-01-30D19043373.63 ppb
2019-01-30D1904336ND
2019-05-08D19211976.52 ppb
2019-05-08D19211983.04 ppb
2019-05-08D1921195ND
2019-05-08D19211963.53 ppb
2019-07-18D19351214.74 ppb
2019-07-18D19351228.36 ppb
2019-07-18D1935123ND
2019-07-18D19351243.80 ppb
2019-09-18D1947011ND
2019-09-18D19470144.15 ppb
2019-09-18D19470136.69 ppb
2019-09-18D19470125.72 ppb
2019-12-31D19645761.67 ppb
2019-12-31D1964575ND
2019-12-31D19645743.66 ppb
2019-12-31D19645734.47 ppb
2020-02-12D20065642.07 ppb
2020-02-12D20065652.68 ppb
2020-02-12D20065636.90 ppb
2020-02-12D20065627.92 ppb
2020-06-02D20253492.12 ppb
2020-06-02D2025348ND
2020-06-02D20253475.55 ppb
2020-06-02D20253466.88 ppb
2020-08-31D2042977ND
2020-08-31D20429765.64 ppb
2020-08-31D20429756.56 ppb
2020-08-31D20429783.24 ppb
2020-10-01D20491635.15 ppb
2020-10-01D20491653.25 ppb
2020-10-01D20491628.17 ppb
2020-10-01D2049164ND
2021-01-20D21029421.81 ppb
2021-01-20D21029403.97 ppb
2021-01-20D2102941ND
2021-01-20D21029395.06 ppb
2021-04-21D21183021.93 ppb
2021-04-21D2118303ND
2021-04-21D21183014.19 ppb
2021-04-21D21183044.10 ppb
2021-08-04D21397503.14 ppb
2021-08-04D2139746ND
2021-08-04D213974914.3 ppb
2021-08-04D21397474.93 ppb
2021-11-09D21608448.66 ppb
2021-11-09D21608454.68 ppb
2021-11-09D21608461.83 ppb
2021-11-09D21608472.10 ppb
2022-02-02D22053078.38 ppb
2022-02-02D22053083.81 ppb
2022-02-02D2205309ND
2022-02-02D22053102.36 ppb
2022-06-09D2227608ND
2022-06-09D22276072.27 ppb
2022-06-09D22276063.93 ppb
2022-06-09D22276057.64 ppb
2022-08-19D2240994ND
2022-08-19T22409934.21 ppb
2022-08-19D22409926.11 ppb
2022-08-19D224099113.6 ppb
2022-11-16D22569822.90 ppb
2022-11-16D2256983ND
2022-11-16D22569842.29 ppb
2022-11-16D225698113.0 ppb
2023-02-01PP2302075-044.16 ppb
2023-02-01PP2302075-031.42 ppb
2023-02-01PP2302075-026.70 ppb
2023-02-01PP2302075-013.11 ppb
2023-05-10PP2309048-017.40 ppb
2023-05-10PP2309048-024.30 ppb
2023-05-10PP2309048-032.30 ppb
2023-05-10PP2309048-042.66 ppb
2023-08-02D2316309-019.70 ppb
2023-08-02D2316309-024.78 ppb
2023-08-02D2316309-03ND
2023-08-02D2316309-043.05 ppb
2023-10-16D2322558-042.40 ppb
2023-10-16D2322558-031.35 ppb
2023-10-16D2322558-028.18 ppb
2023-10-16D2322558-014.01 ppb