Water Cistern Cleaning
After initial construction of the cistern (or placement if cistern is precast, polyethylene or fiberglass) or after any maintenance, the cistern must be flushed to remove any sediment and thoroughly disinfected. This includes pump or float replacement or any plumbing work that has occurred within the cistern. This is a health requirement.
Prior to filling and using a cistern, it must first be cleaned and disinfected. Cleaning, of all types of cisterns, requires sweeping and removing all debris, dirt and dust from the inside of the cistern. If this requires entering the cistern, every precaution must be taken to prevent suffocation and breathing toxic fumes. No cistern should be entered until appropriate measures have been taken to insure the cistern’s air quality is safe. No cistern should be entered unless the person entering the tank has been trained in confined space entry and follows the appropriate safety procedures for entry. It is also recommended that the interior be cleaned with a pressure cleaner.
Disinfection of a cistern can be accomplished by using a solution of household bleach at a concentration of between 100-200 ppm. Common household bleach containing approximately 5% chlorine by weight may be used. Approximately 4 oz. Chlorine per 5 gallons of water will provide the proper concentration. All inside surfaces must be brushed with this solution. Allow a contact time of 12 to 24 hours. The cistern must now be filled with water from a potable water source. Faucets and water taps must be turned on in the dwelling. After the water has run for a few minutes, turn off all the faucets and taps and again let the water stand for 12 to 24 hours. This will disinfect all the water lines of the delivery system.
After the allotted time, the cistern must be emptied and the water lines drained. The chlorinated water used for disinfection must not be discharged to a stream, river or other waterway where damage to aquatic life may occur. The chlorinated water must not be drained to a sewer system. The cistern must now be filled a second time from a potable water source. This water should now be ready for use. If the cistern is constructed from concrete, it may be desirable to use at least 3 loads of water prior to drinking the water. The water may still have a “chalky†appearance and may also have a slight “cement tasteâ€.
It is highly recommended that cistern water be sampled annually for bacteriological contents. Other guidelines would be to drain, clean, and disinfect a cistern approximately every five years, especially if a water sample indicates contamination.