Shock chlorinating a well

When to disinfect

Texas A&M says the usual chlorine sources are dry chlorine or plain liquid household bleach, and warns against scented bleach or bleach with additives.

Texas A&M says the amount of chlorine depends on the depth of standing water in the well, which is the well depth minus the static water level.

The Minnesota Department of Health targets 50 to 200 ppm chlorine in the recirculating water and a contact time of at least two hours, preferably six or overnight.

The Minnesota Department of Health advises retesting two to four weeks after disinfection because coliform can regrow, and repeating the process if it is found.

Texas A&M notes chlorine may damage the rubber bladder in some pressure tanks, so check the manufacturer guide, and bypass carbon and reverse osmosis filters.

Texas guidance from the Texas Agricultural Extension Service says the owner's best option is to hire a licensed pump installer or well driller, because mistakes can damage the casing, plumbing and pump.

Texas A&M's step-by-step bleach method is written for wells with a working submersible pump only; jet pump or damaged systems need a contractor.

Sources: When to shock chlorinate; Target strength and contact time; A licensed pro is the best option; Some pumps need a different method