The Power of Information

National Drinking Water Database


City of Houston Public Works Utilities - Houston, TX


Serves 2,700,000 people

Total trihalomethanes (TTHMs)

Total trihalomethanes constitute the sum of four disinfection byproducts: chloroform, bromodichloromethane, dibromochloromethane, and bromoform.
 
This Drinking Water System
Test Days Exceeding Health GuidelinesDefinition of what this is
37 days
Test Days Exceeding Legal LimitsNumber of days in which the samples taken in that day exceed the Maximum Contaminant Level (Depending on the contaminant and its MCL, that may or may not trigger an MCL violation. Some MCLs are based on averages spanning several months to a year)
0 days
Test DaysNumber of days in which this chemical has reported results in the data we received from the State
51 days
Tests ConductedNumber of individual tests done for this contaminant
460 tests

Testing Summary

ContaminantAverage/
Maximum
Result
Health Limit
Exceeded
Legal Limit
Exceeded

Testing History

-Tested      -Detected      -Over Health Guidelines      -Over Legal Limit*
Total trihalomethanes (TTHMs)Total trihalomethanes constitute the sum of four disinfection byproducts: chloroform, bromodichloromethane, dibromochloromethane, and bromoform.20.11 ppb
69.3 ppb
Yes
9.8 ppb
No
80 ppb
NOTE: Each dot in the above graph represents one month.
* Water utilities are noted as exceeding the legal limit if any test is above the maximum contaminant level (MCL). Most MCLs are based on annual averages so exceeding the MCL for one test does not necessarily indicate that the system is out of compliance.

Health Based and Legal Limits for Total trihalomethanes (TTHMs)

Health Based Limits for Total trihalomethanes (TTHMs)

StandardDescriptionLevel
One in one million (10-6) Cancer RiskThe concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 1,000,000. Source: U.S. Environmental Protection Agency.9.8 ppb
EPA Human Health Water Quality CriteriaWater quality criteria set by the US EPA provide guidance for states and tribes authorized to establish water quality standards under the Clean Water Act (CWA) to protect human health. These are non-enforceable standards based upon exposure by both drinking water and the contribution of water contamination to other consumed foods. Source: U.S. Environmental Protection Agency.11.5 ppb
Maximum Contaminant Limit (MCL)The enforceable standard which defines the highest level of a contaminant that is allowed in drinking water. MCLs are set as close to health-based limits (Maximum Contaminant Level Goals, or MCLGs) as feasible using the best available analytical and treatment technologies and taking cost into consideration. Source: U.S. Environmental Protection Agency.80 ppb
Lifetime health-based limit, non-cancer riskConcentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic health effects for a lifetime of exposure. The Lifetime health-based limit (or Health Advisory, HA) is based on exposure for a a 70-kg adult consuming 2 liters of water per day. Source: U.S. Environmental Protection Agency.130 ppb
One in ten thousand (10-4) Cancer RiskThe concentration of a chemical in drinking water corresponding to an excess estimated lifetime cancer risk of 1 in 10,000. Source: U.S. Environmental Protection Agency.980 ppb
Drinking Water Equivalent LevelA lifetime exposure concentration protective of adverse, noncarcinogenic health effects, that assumes all of the exposure to a contaminant is from drinking water. Source: U.S. Environmental Protection Agency.1835 ppb
Children's health-based limit for 10-day exposureConcentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic effects for up to ten days of exposure. The Ten-Day health-based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day. Source: U.S. Environmental Protection Agency.4860 ppb
Children's health-based limit for 1-day exposureConcentration of a chemical in drinking water that is not expected to cause any adverse, noncarcinogenic health effects for up to one day of exposure. The One-Day health-based limit (or Health Advisory, HA) is typically set to protect a 10-kg child consuming 1 liter of water per day. Source: U.S. Environmental Protection Agency.10600 ppb

Testing Results

Testing DateAverage
Result
Samples taken that dayNumber of Non-DetectsRange of Results
2007-11-0118.14 ppb1510 to 29.2 ppb
2007-10-3120.11 ppb1720 to 29.1 ppb
2007-09-2014.53 ppb1340 to 43.3 ppb
2007-09-1951.16 ppb1001.2 to 203 ppb
2007-08-0942.9 ppb2030.5 to 55.3 ppb
2007-07-260 ppb110 ppb
2007-07-2534.27 ppb1410 to 54.3 ppb
2007-06-0734.32 ppb15015.7 to 50.6 ppb
2007-06-0635.41 ppb1720 to 58 ppb
2007-04-1114.98 ppb1360 to 41.2 ppb
2007-03-2930.73 ppb1710 to 52.9 ppb
2007-03-2833.17 ppb15013 to 45 ppb
2007-02-1512.85 ppb1340 to 42.3 ppb
2007-01-2521.93 ppb1710 to 37 ppb
2007-01-2322.03 ppb1506.4 to 33.1 ppb
2006-12-203.93 ppb400 to 15.7 ppb
2006-12-070.25 ppb400 to 0.5 ppb
2006-10-2615.77 ppb1340 to 60.8 ppb
2006-08-1069.3 ppb1069.3 ppb
2006-07-2012.32 ppb1480 to 44.9 ppb
2006-05-1021.71 ppb1020 to 49.3 ppb
2006-04-1312.15 ppb1370 to 33.8 ppb
2006-02-226.43 ppb400 to 62.2 ppb
2006-02-210.7 ppb400 to 1.4 ppb
2006-02-0811.22 ppb1360 to 39.8 ppb
2005-12-190 ppb400 ppb
2005-11-037.73 ppb1380 to 28 ppb
2005-10-278.23 ppb400 to 49.4 ppb
2005-07-270.06 ppb400 to 1.2 ppb
2005-07-2624.87 ppb1010 to 37.2 ppb
2005-07-2118.28 ppb1360 to 98.7 ppb
2005-07-209.71 ppb400 to 38.7 ppb
2005-05-0517.29 ppb400 to 140 ppb
2005-05-0411.04 ppb400 to 165.7 ppb
2005-04-1416.36 ppb1360 to 55.1 ppb
2005-04-130 ppb400 ppb
2005-01-279.68 ppb1170 to 36.2 ppb
2005-01-2634.85 ppb2034 to 35.7 ppb
2004-11-0411.73 ppb1270 to 42.5 ppb
2004-11-0326.13 ppb1010 to 41.4 ppb
2004-08-1239.39 ppb1002.9 to 65.4 ppb
2004-07-0822.25 ppb1250 to 73.1 ppb
2004-04-2952.6 ppb2052.1 to 53.1 ppb
2004-04-2123.5 ppb2070 to 54.1 ppb
2004-02-2612.01 ppb1570 to 40.6 ppb
2004-01-2826.03 ppb3015.7 to 37.5 ppb
2004-01-2733.95 ppb2030.3 to 37.6 ppb
2004-01-263.9 ppb400 to 11.7 ppb
2004-01-200 ppb400 ppb
2004-01-1433.8 ppb1033.8 ppb
2004-01-1341.9 ppb1041.9 ppb