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Guidelines for Sizing Water Storage Tanks


  • Hotels 1045 Litres (actual capacity) per bedroom per
  • Day Offices 45 Litres (actual capacity) per person per day
  • Schools 36 Litres (actual capacity) per person per day
  • House with 2 bathrooms 682 Litres (actual capacity) per day

The mains pressure must be sufficient to re-fill the tank while the premises are closed. In areas with low water pressure, the above figures would need to be increased. In our experience, the water pressure has been reducing gradually for the past number of years, particularly in the cities and in areas where there have been large developments.

Note: The above figures are based on Dublin Corporation Guide Lines. The minimum requirements do not include for fire-fighting.


Tank Height  % loss in capacity for  51mm (2″) overflow  % loss in capacity for 89mm (3½”)
500 42 51
1000 21 26
1500 14 17
2000 11 13
2500 8 10
3000 7 9
3500 6 7
4000 6 7

The above figures are approximate and are based on a 51mm (2’’) and 89 mm (3 ½ “) overflows. If a larger overflow is used, the percentage loss will be greater.

For more information see our installation & tender guidelines:

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