How to Clean Water Tanks With Chlorine

Cities and towns maintain safe municipal water supplies based on standards established by federal, state and local governments. Emergency aid workers, rainwater collectors and rural farms and homes with independent water storage systems need to keep water clean water on their own. Other reliable, "greener" water purification systems are available, but chlorine disinfection is used worldwide to produce large amounts of safe drinking water as quickly as possible. Disinfecting water transport and storage tanks with chlorine is also the international standard.

Things You'll Need

• Safety glasses
• Safety clothing and gloves
• Stiff scrub brush
• Extension handle, if needed
• Garden hose
• High-pressure hoze nozzle
• High-test hypochlorite (HTH)
• Polyvinyl bucket with handle
• Comparator

Instructions

Clean the Tank

1. Drain the tank. For storage tanks, drain water from the washout valve rather than the usual outlet. Portable tanks may need to be dismantled or tipped.

2. Scrub internal surfaces using detergent and a stiff brush or high-pressure hose, leaving outlet valves open. Clean all surfaces, including corners and joints. If access is a problem, use a brush with an extension handle and scrub from outside the tank.

3. Rinse to remove residue, using a high-pressure hose if available, or close all valves. Fill the tank with water and let stand for at least several hours. Repeat several times if needed.

Disinfect, then Rinse

1. Calculate the tank's total volume, in cubic meters or cubic yards. Fill tank with water until 1/4 full.

2. Prepare a very concentrated chlorine solution using high-test hypochlorite (HTH), the chlorine used in swimming pools. The World Health Organization recommends adding 50 g of HTH to a bucket containing 20L of water (just over 5 gallons). For every cubic meter of tank volume (1 cubic meter equals 1.3 cubic yards) add 1/2 bucket of the concentrated chlorine solution.

3. Slowly pour the chlorine concentrate solution into the tank, mixing well as you pour, and then add clean water until the tank is full.

4. Let tank stand for 24 hours. If the tank is urgently needed, double the amount of chlorine in the bucket and reduce disinfection time to eight hours.

5. Empty the tank, safely disposing of the disinfection solution, then fill it with fresh water and let stand for 30 minutes. Using a comparator, test for residual chlorine. If chlorine residues measure 0.5mg per L or lower, the tank is safe to use again. If residual chlorine is too high, empty the tank and refill it with clean water, let stand for another 30 minutes and test the water again.

Tips & Warnings

• Clean and disinfect any pipes or hoses used in connection with the tank, following the same process outlined above.

• If you prefer using household chlorine bleach to disinfect your water tank, buy a new bottle or two --- bleach is highly reactive and loses potency once opened --- then contact your local health department for recommended dilutions.

• Cleaning and disinfecting solutions may qualify as toxic waste, so follow all safety and environmental regulations.

• Take all possible safety precautions. Make sure someone remains outside the water tank during tank scrubbing and flushing, for example, in case the cleaner inside falls or has some other accident.

• Clean water tanks in an open, remote area, staying well away from homes or businesses.

References

• Who.int: Cleaning and Disinfecting Water Storage Tanks
• Harvesth2o.com: Water Purification Technology: What is "Green" & What is Not
• Cdc.gov: Safe Water Systems Publications--Disinfectant

Resources

• American Water Works Association
• Drinking Water Standards
• Emergency Disinfection of Water