Shock Chlorinating a Private Drinking Water Supply
Sharon O. Skipton, Extension Water Quality Educator
Bruce I. Dvorak, Extension Environmental Infrastructure Engineer
Wayne Woldt, Extension Environmental Engineer
William L. Kranz, Extension Irrigation Specialist
Shock chlorination is the introduction of a strong chlorine solution into the entire water distribution system (well, pump, distribution pipeline, hot water heater, etc.).
Shock chlorination is suggested if test results indicate that coliform, fecal, and/or E-coli bacteria are present in a private drinking water supply. However, shock chlorination should not be a substitute for a potable water supply. Before shock chlorination be sure well construction is adequate to prevent entry of contaminants, and find and eliminate contaminant sources. If the bacterial contamination is recurring, another disinfection process such as continuous chlorination, distillation, ozonation, or ultraviolet radiation is required rather than shock chlorination.
Shock chlorination is also recommended for treatment of iron, manganese, and/or sulfur bacteria. While shock chlorination may not entirely eliminate these nuisance bacteria, it will usually help manage the bacteria for a period of time.
Safety practices
Before beginning the shock chlorination process, fresh water should be run into a five gallon container. If concentrated chlorine accidentally comes in contact with eyes or skin, use this fresh water to flush the affected area for 10-15 minutes. If an individual gets chlorine solution in their eyes, they should see a doctor after thoroughly flushing the affected eye.
A second safety practice is to wear appropriate safety clothing and equipment including goggles to protect eyes, rubber gloves to protect hands, and rubber boots on feet. A waterproof suit, coveralls, or full-length apron can help to prevent discoloration of clothing.
Since the water supply will be temporarily interrupted during the shock chlorination process, having access to an adequate potable water supply will be critical. A water supply for drinking and cooking should be identified for the period between introduction of chlorine to the water system and receiving water test results after completion of the shock chlorination process.
Well chlorination
Chlorine is very volatile so it is dangerous to work with in confined areas. Make sure the work area is well ventilated. Prepare a mixture of one-half gallon of regular household chlorine bleach that contains 5% to 6% sodium hypochlorite per 5 gallons of fresh water. Check the label, or call the manufacturer's toll free number provided on the label for information on the sodium hypochlorite concentration of a specific chlorine product. Bleaches containing fragrances, soaps, or other additives should be avoided for drinking water disinfection. Use this mixture to disinfect the well pit, spring house or other portions of the distribution equipment that may contribute bacteria to the water supply (pump, motor, pressure tank and exposed wiring conduits).
Drain as much water from the system as possible. For systems with pressure tanks containing a bladder, the rubber air-water separator inside the tank could be damaged by the chlorine solution. Check manufacturers' recommendations to determine if the pressure tank should be bypassed. For pressure tanks without bladders, release the air so that the tank can be filled with chlorinated water. Drain water from the water heater so that chlorinated water can be circulated through the hot water pipelines. Check with the manufacturer of water softeners, sediment filters, iron removal filters, activated carbon filters, reverse osmosis filters, or any other water treatment equipment in place prior to shock chlorinating the system.
Use this online calculator to determine the amount of product needed for shock chlorination of your system.
For more detailed information on Shock Chlorination, please see the UNL Extension Publication: Drinking Water Treatment: Shock Chlorination.