A cistern is a device that holds liquid. They come in all shapes and sizes with the primary intention of collecting water. These vessels collect rainwater or other runoff water and store it. The use for this non-potable or "gray" water is for purposes other than drinking. A cistern may be concrete, steel or other materials and may be above or below ground. Cleaning a cistern and removing the bacteria is not difficult, but requires certain equipment for the safety of the person(s) cleaning it out.
Put on all safety equipment before getting into the cistern. Mix ¼ cup of chlorine bleach with 10 gallons of water in a clean bucket.
Scrub the entire surface of the cistern using the scrub brush and handle. Keep the brush saturated by dipping it into the bucket of bleach and water. Be generous with the cleaning solution. Clean the grating thoroughly and rinse it off.
Open the drain on the cistern. Spray the cistern out completely using the garden hose until you no longer small chlorine bleach. Repeat this procedure to clean the cistern at least every five years.
Treat water in the cistern using chlorine to prevent bacteria from growing.
Always wear a respirator when working in enclosed areas. A second person must be outside the tank to monitor and render assistance if fumes overcome the cleaner.