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EWG's Tap Water Database — 2021 UPDATE

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Total trihalomethanes (TTHMs)

California Water Service - South San Francisco

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.

 

335

Samples

0

Samples exceeding legal limit (MCL)

221

Samples exceeding
health guidelines

Testing results - average by year

 
YearAverage resultSamples takenDetectionsRange of results
2013N/A00N/A
201410.9 ppb12358ND - 46.9 ppb
201511.3 ppb9849ND - 41.0 ppb
201644.5 ppb282817.0 ppb - 61.0 ppb
201734.0 ppb303014.0 ppb - 51.0 ppb
201835.8 ppb28289.60 ppb - 47.6 ppb
201936.3 ppb282810.9 ppb - 59.6 ppb

ppb = parts per billion

State and national drinking water standards and health guidelines

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
2014-01-095701-013-0940ND
2014-01-145701-009-11324.20 ppb
2014-01-145701-010-11389.40 ppb
2014-01-145701-011-1130ND
2014-01-285701-013-0922ND
2014-02-045701-013-1006ND
2014-02-055701-009-10313.60 ppb
2014-02-055701-010-101310.3 ppb
2014-02-055701-011-1030ND
2014-02-115701-013-1327ND
2014-02-195701-013-1335ND
2014-02-255701-003-1325ND
2014-02-255701-013-1048ND
2014-03-045701-013-1004ND
2014-03-055701-009-14032.50 ppb
2014-03-055701-010-141019.3 ppb
2014-03-055701-011-1400ND
2014-03-105701-010-135020.8 ppb
2014-03-105701-900-080520.5 ppb
2014-03-105701-901-084522.2 ppb
2014-03-105701-902-103518.3 ppb
2014-03-105701-903-082521.2 ppb
2014-03-105701-904-090525.6 ppb
2014-03-105701-906-101527.8 ppb
2014-03-105701-907-130528.4 ppb
2014-03-115701-013-1340ND
2014-03-165701-013-0937ND
2014-03-185701-006-1048ND
2014-03-185701-007-1100ND
2014-03-185701-008-1037ND
2014-03-185701-014-1021ND
2014-03-275701-013-1038ND
2014-04-035701-013-1130ND
2014-04-085701-013-1100ND
2014-04-155701-009-13293.60 ppb
2014-04-155701-010-133424.8 ppb
2014-04-155701-011-13250.500 ppb
2014-04-155701-013-1117ND
2014-04-295701-013-0910ND
2014-05-055701-013-1134ND
2014-05-145701-013-0842ND
2014-05-205701-009-11213.80 ppb
2014-05-205701-010-113829.4 ppb
2014-05-205701-011-1119ND
2014-05-205701-013-1100ND
2014-05-275701-013-1050ND
2014-06-045701-009-08303.30 ppb
2014-06-045701-010-084023.6 ppb
2014-06-045701-011-0828ND
2014-06-045701-013-1130ND
2014-06-095701-010-134022.5 ppb
2014-06-095701-013-1117ND
2014-06-095701-900-081526.6 ppb
2014-06-095701-901-113021.8 ppb
2014-06-095701-902-135024.8 ppb
2014-06-095701-903-111526.0 ppb
2014-06-095701-904-114525.3 ppb
2014-06-095701-906-141521.7 ppb
2014-06-095701-907-110033.9 ppb
2014-06-175701-013-1125ND
2014-07-095701-013-1011ND
2014-07-155701-013-1136ND
2014-07-165701-009-11273.10 ppb
2014-07-165701-010-113835.5 ppb
2014-07-165701-011-1124ND
2014-07-225701-013-1140ND
2014-07-295701-013-1137ND
2014-08-055701-013-1530ND
2014-08-135810-009-08405.40 ppb
2014-08-135810-010-085023.0 ppb
2014-08-135810-011-08375.40 ppb
2014-08-135810-013-0815ND
2014-08-185701-013-1103ND
2014-08-265701-013-1126ND
2014-09-035701-013-1027ND
2014-09-085701-013-1025ND
2014-09-115701-010-085736.8 ppb
2014-09-115701-900-110744.6 ppb
2014-09-115701-901-105134.9 ppb
2014-09-115701-902-112233.7 ppb
2014-09-115701-903-090831.5 ppb
2014-09-115701-904-094334.5 ppb
2014-09-115701-906-103623.9 ppb
2014-09-115701-907-092446.0 ppb
2014-09-165701-009-09123.30 ppb
2014-09-165701-010-094046.9 ppb
2014-09-165701-011-0910ND
2014-09-165701-013-0855ND
2014-09-235701-013-1330ND
2014-09-255701-006-1321ND
2014-09-255701-007-1328ND
2014-09-255701-008-1313ND
2014-09-255701-014-1355ND
2014-10-025701-009-11134.10 ppb
2014-10-025701-010-111842.7 ppb
2014-10-025701-011-1112ND
2014-11-045701-013-1111ND
2014-11-125701-009-13202.40 ppb
2014-11-125701-010-133729.7 ppb
2014-11-125701-011-1318ND
2014-11-125701-013-1107ND
2014-11-185701-013-1122ND
2014-11-195701-003-1111ND
2014-11-245701-013-1320ND
2014-12-025701-013-0911ND
2014-12-045701-009-13432.60 ppb
2014-12-045701-010-135631.0 ppb
2014-12-045701-011-1342ND
2014-12-085701-010-071733.5 ppb
2014-12-085701-900-071734.9 ppb
2014-12-085701-901-071734.4 ppb
2014-12-085701-902-071729.9 ppb
2014-12-085701-903-071737.5 ppb
2014-12-085701-904-071735.9 ppb
2014-12-085701-906-071744.7 ppb
2014-12-085701-907-071744.6 ppb
2014-12-095701-013-1022ND
2014-12-165701-013-1416ND
2014-12-175701-006-1025ND
2014-12-175701-007-1032ND
2014-12-175701-008-1004ND
2014-12-219590-013-1430ND
2014-12-309590-013-1035ND
2015-01-055701-013-1330ND
2015-01-075701-009-11352.70 ppb
2015-01-075701-010-114618.9 ppb
2015-01-075701-011-1132ND
2015-01-135701-013-1101ND
2015-01-205701-013-1100ND
2015-01-265701-013-1029ND
2015-02-025701-013-1034ND
2015-02-115701-009-09022.60 ppb
2015-02-115701-010-091123.2 ppb
2015-02-115701-011-0900ND
2015-02-115701-013-0920ND
2015-02-115701-014-1033ND
2015-02-175701-013-0952ND
2015-02-185701-003-1040ND
2015-02-235701-013-1101ND
2015-03-035701-013-1342ND
2015-03-045701-009-09382.50 ppb
2015-03-045701-010-094831.1 ppb
2015-03-045701-011-0939ND
2015-03-105701-010-093725.8 ppb
2015-03-105701-013-1355ND
2015-03-105701-900-093929.1 ppb
2015-03-105701-901-093924.0 ppb
2015-03-105701-902-093927.1 ppb
2015-03-105701-903-093727.9 ppb
2015-03-105701-904-093729.8 ppb
2015-03-105701-906-093910.7 ppb
2015-03-105701-907-093739.8 ppb
2015-03-165701-013-1121ND
2015-03-195701-006-1041ND
2015-03-195701-007-1053ND
2015-03-195701-008-1021ND
2015-03-245701-013-1117ND
2015-03-315701-013-1310ND
2015-04-075701-009-14052.60 ppb
2015-04-075701-010-143025.0 ppb
2015-04-075701-011-1400ND
2015-04-075701-013-1340ND
2015-04-145701-013-1435ND
2015-04-225701-013-1334ND
2015-04-285701-013-0950ND
2015-05-069590-009-14251.70 ppb
2015-05-069590-010-150226.0 ppb
2015-05-069590-011-1421ND
2015-05-069590-013-1400ND
2015-05-139590-013-1321ND
2015-05-195701-013-1039ND
2015-05-215701-003-1336ND
2015-05-265701-013-1136ND
2015-05-275701-014-1332ND
2015-06-015701-013-1130ND
2015-06-025701-009-10062.60 ppb
2015-06-025701-010-101722.4 ppb
2015-06-025701-011-1005ND
2015-06-095701-013-1000ND
2015-06-155701-010-075929.7 ppb
2015-06-155701-013-1352ND
2015-06-155701-900-075932.8 ppb
2015-06-155701-901-075925.8 ppb
2015-06-155701-902-075925.1 ppb
2015-06-155701-903-075926.4 ppb
2015-06-155701-904-075928.3 ppb
2015-06-155701-906-075911.1 ppb
2015-06-165701-907-085532.3 ppb
2015-06-185701-006-1142ND
2015-06-185701-007-1428ND
2015-06-185701-008-1455ND
2015-06-235701-013-1005ND
2015-06-305701-013-0915ND
2015-07-065701-013-0909ND
2015-07-075701-009-11262.40 ppb
2015-07-075701-010-131719.7 ppb
2015-07-075701-011-1124ND
2015-08-265701-003-1410ND
2015-08-265701-006-1420ND
2015-09-165701-010-083228.7 ppb
2015-09-165701-900-083227.3 ppb
2015-09-165701-901-083227.7 ppb
2015-09-165701-902-083229.4 ppb
2015-09-165701-903-083227.8 ppb
2015-09-165701-904-083227.0 ppb
2015-09-165701-906-083212.6 ppb
2015-09-165701-907-083221.2 ppb
2015-11-165701-003-1320ND
2015-11-165701-006-1327ND
2015-11-165701-009-13362.30 ppb
2015-11-165701-010-114127.2 ppb
2015-11-165701-011-13390.500 ppb
2015-11-185810-014-1111ND
2015-12-155701-900-080326.9 ppb
2015-12-155701-901-080329.1 ppb
2015-12-155701-902-080326.9 ppb
2015-12-155701-906-080329.6 ppb
2015-12-165810-010-125938.0 ppb
2015-12-165810-903-103236.0 ppb
2015-12-165810-904-114635.0 ppb
2015-12-165810-907-110341.0 ppb
2016-03-155701-900-082438.5 ppb
2016-03-155701-901-082439.8 ppb
2016-03-155701-902-082430.8 ppb
2016-03-155701-903-082435.4 ppb
2016-03-155701-904-082434.0 ppb
2016-03-155701-906-082453.0 ppb
2016-03-155701-907-082455.0 ppb
2016-06-135701-900-142355.1 ppb
2016-06-135701-901-142349.8 ppb
2016-06-135701-902-142349.1 ppb
2016-06-135701-903-142351.4 ppb
2016-06-135701-904-142348.7 ppb
2016-06-135701-906-142323.7 ppb
2016-06-135701-907-142355.8 ppb
2016-09-145701-900-082750.1 ppb
2016-09-145701-901-082744.9 ppb
2016-09-145701-902-082751.0 ppb
2016-09-145701-903-082748.3 ppb
2016-09-145701-904-082746.0 ppb
2016-09-145701-906-082726.7 ppb
2016-09-145701-907-082749.6 ppb
2016-12-125810-900-140361.0 ppb
2016-12-125810-901-131247.0 ppb
2016-12-125810-902-134659.0 ppb
2016-12-125810-903-142547.0 ppb
2016-12-125810-904-143746.0 ppb
2016-12-125810-906-133117.0 ppb
2016-12-125810-907-141633.0 ppb
2017-03-155810-900-103320.0 ppb
2017-03-155810-901-102118.0 ppb
2017-03-155810-902-104720.0 ppb
2017-03-155810-906-110019.0 ppb
2017-03-165701-903-092035.9 ppb
2017-03-165701-904-092014.0 ppb
2017-03-165701-907-092034.5 ppb
2017-06-025701-902-132143.0 ppb
2017-06-025701-904-131438.7 ppb
2017-06-125701-900-080027.0 ppb
2017-06-125701-901-080033.6 ppb
2017-06-125701-902-080034.2 ppb
2017-06-125810-903-100531.0 ppb
2017-06-125810-904-112536.0 ppb
2017-06-125701-906-080020.8 ppb
2017-06-125810-907-094526.0 ppb
2017-09-125810-900-091045.0 ppb
2017-09-125810-901-094050.0 ppb
2017-09-125810-902-082042.0 ppb
2017-09-125810-903-093046.0 ppb
2017-09-125810-904-095051.0 ppb
2017-09-125810-906-100547.0 ppb
2017-09-125810-907-084051.0 ppb
2017-12-145701-900-082528.5 ppb
2017-12-145701-901-082532.7 ppb
2017-12-145701-902-082532.6 ppb
2017-12-145810-903-112243.0 ppb
2017-12-145810-904-111043.0 ppb
2017-12-145701-906-082516.8 ppb
2017-12-145810-907-114741.0 ppb
2018-03-145701-900-083626.1 ppb
2018-03-145701-901-083626.8 ppb
2018-03-145701-902-083627.2 ppb
2018-03-145701-903-083627.5 ppb
2018-03-145701-904-083627.9 ppb
2018-03-145701-906-083613.1 ppb
2018-03-145701-907-083627.5 ppb
2018-06-115701-900-085344.3 ppb
2018-06-115701-901-085344.1 ppb
2018-06-115701-902-085345.3 ppb
2018-06-115701-903-085344.2 ppb
2018-06-115701-904-085344.5 ppb
2018-06-115701-906-085314.9 ppb
2018-06-115701-907-085346.5 ppb
2018-09-115701-900-081846.0 ppb
2018-09-115701-901-081845.7 ppb
2018-09-115701-902-081846.3 ppb
2018-09-115701-903-081847.4 ppb
2018-09-115701-904-081846.9 ppb
2018-09-115701-906-081822.0 ppb
2018-09-115701-907-081847.6 ppb
2018-12-125701-900-091937.3 ppb
2018-12-125701-901-091938.7 ppb
2018-12-125701-902-091939.5 ppb
2018-12-125701-903-091940.0 ppb
2018-12-125701-904-091935.8 ppb
2018-12-125701-906-09199.60 ppb
2018-12-125701-907-091938.9 ppb
2019-03-125701-900-090011.7 ppb
2019-03-125701-901-090013.7 ppb
2019-03-125701-902-090013.0 ppb
2019-03-125701-903-090014.9 ppb
2019-03-125701-904-090015.3 ppb
2019-03-125701-906-090011.2 ppb
2019-03-125701-907-090015.7 ppb
2019-06-125701-900-092259.3 ppb
2019-06-125701-901-092258.0 ppb
2019-06-125701-902-092256.4 ppb
2019-06-125701-903-092254.5 ppb
2019-06-125701-904-092254.0 ppb
2019-06-125701-906-092256.3 ppb
2019-06-125701-907-092259.6 ppb
2019-09-105701-900-080042.8 ppb
2019-09-105701-901-084045.1 ppb
2019-09-105701-902-092045.8 ppb
2019-09-105701-903-083045.0 ppb
2019-09-105701-904-085044.4 ppb
2019-09-105701-906-104014.9 ppb
2019-09-105701-907-081542.5 ppb
2019-12-125701-900-073137.6 ppb
2019-12-125701-901-084039.1 ppb
2019-12-125701-902-085638.6 ppb
2019-12-125701-903-082837.7 ppb
2019-12-125701-904-081639.8 ppb
2019-12-125701-906-093510.9 ppb
2019-12-125701-907-080039.0 ppb