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Cistern Capacity Calculator

Select your cistern requirements below.

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British Standard BS 6700:1997 advises the following guide recommendations for accessing a cisterns storage for various service applications.

Item Recommended Usage Litres Minimum Storage Req - Litres
Actual Usable Cistern Capacity Nominal Cistern Size "Shallow" Nominal Cistern Size "Deep"
Storage Cistern
Break/Booster Tank

Results

British Standard BS 6700:1997 advises the following guide recommendations for accessing a cisterns storage for various service applications.

Usage Actual Usable Cistern Capacity Litres Nominal Cistern Size Litres Shallow Nominal Cistern Size Litres Deep
24 Hour Filling
Night Time filling Only

Notes

Cistern calculation information

The capacity values obtained from the calculator are advisory only.

The calculator advises a cisterns Actual Useable Capacity. (The toal useable volume of water available in the cistern) and dependant on its height, the cistern's estimated nominal capacity based on application.

A cistern's nominal capacity is its total internal volume calculated by multiplying its length x width x height.

For shallow cisterns, 1m or so deep, a significant proportion of nominal capacity is lost resultant on accommodating the height requirement of float valve, overflow fittings and position of outlet connection. A minimum loss of 25% in nominal capacity is to be expected. THis could increase, possibly to 60%, if large float valves and corresponding outlets are fitted as for break tank or booster pump set duties.

The greater the height of a cistern, for any given inlet size, the greater is its proportion of actual useable capacity available. Cisterns 3 to 4m in height will suffer only a modest 10-15% loss of nominal capacity and possibly only up to 30% when break tank and booster pump set duties are required.

Having determined a cisterns nominal size, whether it be shallow (1-2m) or deep (3-4m), the most appropriate cistern length, width and height can be determined based on space availability at the actual site location.

The break or booster tank sizing advised is a minimum buffer capacity only. No strategic storage is allowed for and its function is only in providing an anti-siphon pressure break or as a feed tank to a booster pump. Pump feed connections must not be rated greater than 1.5 m/s to minimise noise within buildings and inlet pipes must be sized to ensure inlet flow rates are always less than pump delivery capacities under all conditions.