The drinking water delivered by DC Water contains chloramines, chemical compounds made from ammonia and chlorine. Chloramine is added to drinking water to kill bacteria and microorganisms in the treatment plant and the distribution system.

As part of the Total Coliform Rule, the EPA requires DC Water to collect over 200 samples a month and test for total chlorine concentration. The EPA requires detection of chlorine in each sample, or greater than 0.0 mg/L total chlorine. The EPA also requires water systems to maintain the annual average at or below 4.0 mg/L. The graph below displays the average concentration of those samples over the past year.