Hurricane Response Guide for Environmental Public Health Professionals
7. Add the disinfectant by filling the tank a quarter full of clean water and sprinkling 80 grams of granular high-strength calcium hypochlorite (HSCH) per 1000 liters of tank capacity. Fill the tank completely, close the lid, and let it stand for 24 hours (or 8 hours if the chlorine quantity was doubled). 8. If the tank has a pump, circulate the disinfectant mixture through the hoses and pump for an hour, then repeat with clean water. If no pump is present, fill the hoses with disinfectant and let them stand for 24 hours before emptying and flushing with clean water. 9. Empty the tank, dispose of the disinfecting water safely, fill the tank with drinking water, let it stand for 30 minutes, then empty it again. The tank is now ready for use. When selecting tanks for water storage, consider their normal use, ease of cleaning, and overall hygiene. Tanks that previously held water but have been out of use must undergo this thorough cleaning and disinfection process before being put back into service. Cleaning and Disinfecting of Cisterns 1. If the cistern is connected to any water treatment units, close valves to those units. Follow manufacturer recommendations to disinfect the treatment system. 2. Add 3 cups (a little less than 1 liter) of 5% - 9% unscented liquid household bleach for every 100 gallons (about 380 liters) of water in the holding cistern.
Cistern Size (gallons)
Tank is ¼ full
Tank is ½ full
Tank is ¾ full
Full Tank
200 450 600
1.5 cups 3.5 cups 4.5 cups 7.5 cups
3 cups 7 cups 9 cups
4.5 cups 10.5 cups 13.5 cups 22.5 cups
6 cups
14 cups 18 cups 30 cups
1,000
15 cups
Table adapted from CDC “Cisterns Before and After a Disaster.”
3. If the cistern is connected to indoor plumbing, open each faucet and run the water until you smell chlorine (bleach). 4. Turn off all faucets and allow the solution to remain in the cistern and plumbing for at least 12 hours. 5. Drain all water from the cistern. 6. Refill the cistern with clean, safe water. 7. Open each faucet and run the water until you do not smell chlorine (bleach). If your cistern uses untreated water and has open connections (for example, gutters and overflows), you might need to drain and clean your cistern. Ask your local health department whether this is needed. If so, use the following steps: 1. Remove all debris from the catchment or drainage area. 2. Remove all debris and water from the cistern. 3. If you can do it safely, scrub the inside of the cistern with a stiff brush and a solution of 1 cup (about 0.25 liter) of unscented liquid household bleach (5%–9% sodium hypochlorite) mixed with 10 gallons (about 38 liters) of water. 4. Rinse the cistern with clean water, then drain. 5. Refill the cistern.
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