Chlorination of Water Tanks For Water Hygiene
Water storage tanks are an important resource in a lot of buildings. They provide continuity of water supply at continuous pressure and act to fill peak high flow demands not feasible directly from the mains. They are also helpful where mains supplies need to be protected from possible backflow.
However, water storage tanks can become soiled and contaminated with both debris and microorganisms and once this occurs they can become a breeding area for unsafe bacteria such as E. coli, coliform bacteria, and Legionella. Legionella control is especially important as Legionella can cause a potentially deadly disease known as Legionnaires’ Disease.
Water storage tanks should be frequently cleaned and disinfected to eliminate this dirt and harmful microorganisms. The procedure is relatively easy but does require specialist help if the tanks are large.
The water storage tank is initially drained to get rid of all the water. Submersible pumps may be utilized if no drain valves are accessible on the tank. Once the tank is empty, it should be physically cleaned to remove debris and dirt. This should be carried out using only clear water and detergents must not be used. The tank must be fully vacuumed out to eliminate all traces of contamination. Once clean the tank is prepared for the disinfection phase. This is usually carried out using chlorine through a process known as chlorination.
The tank should be filled with fresh, clear water and chlorine added to the water. The chlorine generally used is sodium hypochlorite, a liquid. Care needs to be taken when handling sodium hypochlorite, as it is dangerous. Sufficient chlorine is added to give 50 ppm of chlorine within the tank. The ball valve and above the waterline also require chlorination and this is usually performed by spraying a high concentration (1000 ppm) chlorine solution directly onto the tank surface.
The water is allowed to stand in the tank for 1 hour and the system is then classed as having been chlorinated. At this point, sodium thiosulphate crystals might be added to remove the chlorine if large volumes of chlorinated water could cause problems with sewerage. The tank is then drained and refilled with clean water. see this website
If using an external contractor, a chlorination certificate will be provided to certify that the chlorination has been carried out to the appropriate standards and that the tank is clean and ready for use. Microbial analysis should also be performed.
A clean tank ensures that the water within it will not become contaminated and will continue to be safe for use. Ideally, tanks should be examined at least annually and then cleaned if necessary.