In the majority of cases cold water should only be stored in circumstances where:
the mains supply is insufficient to meet the needs of the building population during periods of high demand
building use would be compromised by disruption to the water supply
mains pressure cannot be maintained above a certain height (usually around 3-5 storey’s but can be up to 8 or 9 in some locations)
the installed hot water services require a low pressure cold water supply
It is not unusual to discover stored cold water that could be removed and outlets fed direct from the mains. Where buildings are over 20 years old and original cold water storage tanks are in poor condition it is reasonable to make these redundant and/or switch fully or partially to mains. Older cisterns are often oversized due to specifications at design.