Our friends over at Prince of Petworth recently asked the question “Why does a swimming pool come out of my faucet?” and an anonymous commenter delivered the news: From February 1st until May 17th, DC WASA changed the disinfectant used in its water treatment process from chloarmine (NH2Cl) to chlorine.
Chloramine is used for most of the year because it is far more stable than free chlorine and lacks the smell of chlorine. Chloramine is toxic to certain animals (e.g. fish) and is one of the reasons you need to age the water a few days or use product to make it safe. However, Chloramine is not as effective at sanitizing as free Chlorine. So WASA is effectively shocking the system.
You can read the DC WASA press release for more info