It is important that people follow certain guidelines if they plan on using cold water storage cisterns for drinking water. Water if not stored properly can become stale or unsafe for drinking purposes.
For drinking purposes, the water tank should not be too large. Ideally, the cistern should be no larger than 5 gallons. Having a cold water tank this size helps keep the water fresh as it is replenished frequently. Should water be left standing in the cistern for a period of time due to a house being unoccupied, then the tank should be flushed out with fresh water.
Cold water storage cisterns used for drinking water need a properly fitting lid. The lid should block out light and fit in such a way as to keep vermin, dust and any other contaminates out of the water supply. In addition to a lid, the tank should be fitted with vents, including an overflow vent with screens to keep out pests and foreign particles.
The cold water cistern needs to be insulated and stored in a cool place. The ideal temperature should not be more than 20-degrees C.
Finally, cold water storage cisterns used for drinking water need to be inspected and cleaned on a yearly basis. Any debris in the water tank should be removed and the vessel should be thoroughly cleaned and disinfected. Trash left in a cistern can provide a place for bacteria to thrive.
Water storage tanks and cisterns defar.gov.uk