The spring chlorine switch, and why your water suddenly tastes like a pool

For most of the year the water in this region is disinfected with chloramine, which is chlorine combined with ammonia. Each spring it switches to free chlorine for several weeks while crews flush the mains. Free chlorine is faster acting, which is what you want when flushing stirs sediment out of the pipes. It also smells and tastes far more like a swimming pool, which is why the calls start.

The 2026 dates

The programme covers the areas supplied by the Washington Aqueduct, the Army Corps plant that treats Potomac water for the District, Arlington and Falls Church, plus the part of Fairfax County it reaches. How that supply arrangement works. Utilities on other sources run their own flushing schedules.

The two groups who genuinely need to act

For almost everyone this is a taste event and nothing more. Two exceptions are worth stating clearly, because the products involved are not interchangeable:

• People on home dialysis. Dialysis water treatment has to remove the disinfectant, and free chlorine and chloramine are removed differently. Centres adjust for the switch. If you dialyse at home, confirm your protocol with your care team before the switch period.
• Anyone with fish, reptiles or a pond. Both chloramine and free chlorine are lethal to fish, and a dechlorinator formulated for one is not automatically right for the other. Check the label before the switch rather than after.

What helps with the taste

• Refrigerate a pitcher, loosely covered. Much of the chlorine off-gasses within a few hours, which is the cheapest fix there is.
• Any fresh carbon filter, pitcher, faucet-mount or fridge. Carbon handles chlorine taste well. If yours is not helping, the cartridge is almost certainly overdue: the 2-month rule.
• Run the cold tap for a moment after flushing crews have worked your street, and avoid doing laundry if the water looks discoloured, since sediment stirred up by flushing can stain.

The part worth understanding

Chlorine in drinking water is not a flaw in the system, it is the reason the system works. The trade is that chlorine reacts with natural organic matter in river water and forms disinfection byproducts, which are the contaminants that dominate almost every water report in this region, including Fairfax, DC and Arlington.

That is a real trade-off and not a scandal: the alternative to disinfecting is waterborne disease. But it is the reason the byproducts are worth knowing about, and the reason a Reverse Osmosis (RO) system or a good carbon filter at the drinking tap is a reasonable thing to want. The longer version of the chlorine story.

Dates above are the published 2026 schedule. The programme runs every spring, and the exact dates shift year to year; your utility announces them before the switch begins.