FAQ: Is there a regulatory standard for chlorine or chloramine chemicals in drinking water?
Drinking water utilities that use chlorination or chloramination are required by law to sample water throughout their distribution system, average the total THM measurements, and report the results to the Division of Drinking Water. The Maximum Contaminant Level (MCL) permissible for total THMs in drinking water by California and federal law is currently an average of 80 parts per billion (ppb) over four consecutive quarters. In other words, a utility has not violated the standard unless the average system-wide level over the past year is more than 80 ppb. There are no standards currently for the individual trihalomethanes.