EWG's Tap Water Database — 2019 UPDATE


Total trihalomethanes (TTHMs)

York Water Company

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.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results
201229.1 ppb252514.9 ppb - 47.2 ppb
201324.6 ppb282811.8 ppb - 68.0 ppb
201422.9 ppb161611.4 ppb - 31.8 ppb
201524.7 ppb161610.3 ppb - 35.2 ppb
201628.8 ppb202014.2 ppb - 46.0 ppb
201730.4 ppb202013.0 ppb - 52.0 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
2012-02-09CHAZS E. PRO14.9 ppb
2012-05-07CHAZS, E PRO21.2 ppb
2012-05-07STEWARTSTOWN21.2 ppb
2012-05-07YORKHANA TUR24.7 ppb
2012-05-07HOKE MILL24.8 ppb
2012-05-07W MANCESTER23.6 ppb
2012-05-07N YORK PUMPH25.4 ppb
2012-05-07MT ZION PUMP23.9 ppb
2012-05-07LOGANVILLE P20.6 ppb
2012-08-07CHAZS E. PRO43.7 ppb
2012-08-07STEWARTSTOWN47.2 ppb
2012-08-07YORKANA TURK40.7 ppb
2012-08-07HOKE MILL AB44.7 ppb
2012-08-07W. MANCHESTE35.6 ppb
2012-08-07N. YORK PUMP46.2 ppb
2012-08-07MT ZION PUMP44.9 ppb
2012-08-07LOGANVILLE P33.9 ppb
2012-11-07CHAZS E PROS29.3 ppb
2012-11-07STEWARTSTOWN26.5 ppb
2012-11-07YORKANA TURK25.4 ppb
2012-11-07HOKE MILL AB26.3 ppb
2012-11-07W MANCHESTER19.9 ppb
2012-11-07N YORK PUMPH21.5 ppb
2012-11-07MT ZION PUMP22.7 ppb
2012-11-07LOGANVILLE P19.5 ppb
2013-02-07HOKE MILL AB15.2 ppb
2013-02-07W MANCHESTER12.1 ppb
2013-02-08CHAZS E PROS15.0 ppb
2013-02-08YORKANA TURK13.6 ppb
2013-02-08N YORK PUMPH11.9 ppb
2013-02-08MT ZION PUMP11.8 ppb
2013-02-08LOGANVILLE P12.4 ppb
2013-02-11STEWARTSTOWN14.6 ppb
2013-05-07CHAZS E PROS19.2 ppb
2013-05-07STEWARTSTOWN19.6 ppb
2013-05-07YORKANA TURK20.9 ppb
2013-05-08HOKE MILL19.9 ppb
2013-05-08W MANCHESTER15.7 ppb
2013-05-08N YORK PUMPH18.2 ppb
2013-05-08MT ZION PUMP18.3 ppb
2013-05-08LOGANVILLE P15.4 ppb
2013-08-07HOKE MILL38.8 ppb
2013-08-08W MANCHESTER30.8 ppb
2013-08-08N YORK PUMPH34.8 ppb
2013-08-08MT ZION PUMP35.6 ppb
2013-08-09CHAZS E PROS39.7 ppb
2013-08-09YORKANA TURK36.6 ppb
2013-08-12STEWARTSTOWN68.0 ppb
2013-08-12LOGANVILLE P44.2 ppb
2013-11-07STEWARTSTOWN29.1 ppb
2013-11-07W MANCHESTER24.2 ppb
2013-11-07LOGANVILLE P23.4 ppb
2013-11-11CHAZS E PROS29.3 ppb
2014-02-1114021711-00215.4 ppb
2014-02-1114021711-00411.4 ppb
2014-02-1214021711-00120.4 ppb
2014-02-1214021711-00313.8 ppb
2014-05-0714052045-00131.8 ppb
2014-05-0814052045-00227.9 ppb
2014-05-0814052045-00322.8 ppb
2014-05-0814052045-00422.6 ppb
2014-08-1114081341-00127.6 ppb
2014-08-1114081341-00229.1 ppb
2014-08-1114081341-00324.3 ppb
2014-08-1114081341-00423.6 ppb
2014-11-0714110761-00125.9 ppb
2014-11-0714110761-00225.6 ppb
2014-11-0714110761-00423.3 ppb
2014-11-0714110761-00321.1 ppb
2015-02-101249758214.0 ppb
2015-02-101249759410.3 ppb
2015-02-111249757616.5 ppb
2015-02-111249758810.5 ppb
2015-05-081286392523.7 ppb
2015-05-111286393125.2 ppb
2015-05-111286393723.7 ppb
2015-05-111286394321.4 ppb
2015-08-111324644235.2 ppb
2015-08-111324644833.9 ppb
2015-08-111324645431.3 ppb
2015-08-111324646029.1 ppb
2015-11-101361562934.3 ppb
2015-11-101361563532.1 ppb
2015-11-101361564125.1 ppb
2015-11-101361564728.1 ppb
2016-02-101396769119.2 ppb
2016-02-101396769718.4 ppb
2016-02-101396770314.2 ppb
2016-02-101396770915.7 ppb
2016-05-061438402919.5 ppb
2016-05-111438404029.2 ppb
2016-05-111438404621.1 ppb
2016-05-111438403424.2 ppb
2016-08-101488464336.1 ppb
2016-08-101488465339.4 ppb
2016-08-101488465832.7 ppb
2016-08-101488464834.8 ppb
2016-08-301505595340.2 ppb
2016-08-301505595635.5 ppb
2016-08-311505596246.0 ppb
2016-08-311505596833.8 ppb
2016-11-071534857531.2 ppb
2016-11-071534859329.8 ppb
2016-11-091534858131.5 ppb
2016-11-101534858723.1 ppb
2017-02-071577374517.5 ppb
2017-02-071577375113.0 ppb
2017-02-071577373313.5 ppb
2017-02-081577373918.3 ppb
2017-05-091623458228.1 ppb
2017-05-091623457143.6 ppb
2017-05-091623457631.6 ppb
2017-05-091623458734.2 ppb
2017-08-081670572952.0 ppb
2017-08-101670574147.3 ppb
2017-08-101670573534.6 ppb
2017-08-101670574740.3 ppb
2017-11-081714274137.3 ppb
2017-11-081714278328.7 ppb
2017-11-081714276526.4 ppb
2017-11-081714275926.2 ppb
2017-11-081714277128.1 ppb
2017-11-081714277726.2 ppb
2017-11-091714274731.2 ppb
2017-11-091714275330.1 ppb