Some useful chlorination formulas

• These recommendation are from the Private Water System Handbook, Midwest Plan Service, Iowa State University, MWPS-14, 1992

• All of these formulas are for common household bleach, like Clorox, Purex, or a generic brand. The label should indicate that the bleach contains between 5-6% Sodium Hypochlorite. Do not use bleach with additives or special scents -- just plain laundry bleach.

Disinfectant solution for cleaning surfaces, such as the inside of a holding tank, cistern, or spring box.

"After construction, cleaning, or maintenance, flush the cistern thoroughly with water to remove sediment. Use a stiff brush or broom to thoroughly wash all inside surfaces. One recommenced disinfecting solution is 1/4 cup of 5.25% chlorine laundry bleach in 10 gal water. (MWPS-14, p. 18)

NOTE: Do not go into a holding tank (or septic tank) without positive air flow -- toxic gasses can settle in these tanks. If possible, do not go in the tank at all.

Shock chlorinating a large volume of water.

To make a chlorine concentration of about 200 mg/l (which is the same a 200 ppm) add 3 pints of 5% chlorine bleach to 100 gal water. (MWPS-14,p. 55)

NOTE: If you need to disinfect water in a holding tank, you may consider draining the tank, cleaning as described above, and then refilling it with sanitary water (like from a well that is free of bacteria).

If your system is plumbed such that you must shock chlorinate the water in the holding tank to disinfect your drinking water system, then clean out the tank as much as possible before shocking the system.

*Remove debris and sediment (try a wet-dry vacuum)
*Scrub the walls with a very strong chlorine solution (1/2 gallon chlorine laundry beach per 5 gallons of water)
*Pump the system to remove the water with suspended matter from the holding tank
*Then add bleach to water in tank to shock chlorinate.

Disinfecting a large volume of water for emergency use

First, chlorination isn't effective if the water isn't already fairly clean, so don't bother trying this if the water is cloudy or has a lot of suspended matter in it.

Add 8 cups (1/2 gallon) of chlorine bleach for each 1000 gallons of water. Mix thoroughly and let it stand for 30 minutes. If the water does not have a slight chlorine smell, repeat the dosage and wait another 15 minutes. If after the second dosing, the water still does not have a chlorine odor, it isn't suitable as a drinking water source. If the chlorine taste is too strong, let it stand exposed to the air or pour if from one container to another several times. (MWPS-14, p. 55)

You may be able to use the water source if you filter it first. Pour a gallon of water through a paper filter or clean clothe. To treat one gallon of water use 10 drops of chlorine bleach, mix, wait 30 minutes, smell for chlorine. If no odor, repeat the treatment. If after the second dose of bleach, there is still no odor, don't consume the water.