The fresh water supply system in a building often includes a sump tank and a roof tank. These storage tanks should be cleansed regularly in order to prevent the accumulation of dirt and rust which might lead to chokage of water meters and discoloured water. This leaflet tells you the steps to cleanse these water tanks properly and recommends the frequency of cleansing.

Steps

1. Close the inlet and outlet valves of the water tank;
2. empty the water tank through the washout pipe;
3. thoroughly scrub and cleanse the water tank and the inlet/out pipes with fresh water;
4. drain away the water through the washout pipe;
5. scrub the water tank thoroughly with a solution of chloride of lime or bleaching powder containing not less than 50 parts of chlorine in one million parts of water (a 50 parts per million chlorine solution can be prepared by mixing 15 grams of chloride of lime or bleaching powder in 100 litres of water if the chloride of lime or bleaching powder contains 33% of available chlorine in weight);
6. rinse the water tank thoroughly with fresh water;
7. drain away the water through the washout pipe;
8. open the inlet valve to refill the water tank with fresh water;
9. open the outlet valve, and the water tank is ready for use.

Frequency of Cleansing

The fresh water storage tanks should be cleansed once every three months or more frequently if necessary.