Lift pump for tower blocks
Lift pump
High pressure lift pumps recently fitted to a series of Tower blocks in Portsmouth.

The Problem with Water Pressure

Ongoing water pressure reduction in various water company areas mean that many high rise properties will no longer receive mains water beyond the 3rd floor.

The recognised minimum pressure that a water company must supply to the consumers stop tap is approximately 1bar. That is enough pressure to supply water up to 10 metres height from the stop tap in the street. The minimum flow rate is also10 litres per minute.

Water companies have their own minimum standards and these are usually in the region of 2 bar or 20 metres of head. This provides customers with sufficient water pressure to enable items such as combi boilers and other devices to work. If water pressure drops below 1 bar many pressurised devices will not function correctly.

When calculating the amount of pressure required, the height and initial pressure must be considered. The average storey in a house or block of flats is in the order of 2.5 metres. Thus with a two storey house with a header tank in the roof, the ball valve will receive whatever the head of water is at the main stop tap less about 6 metres of head (0.6bar).

In the case of say a three storey block of flats being supplied water at 1 bar, the kitchen taps in each flat will run at about 0.9, 0.65 and 0.4 bar respectively as we go up. With the lower pressure in the upper flats a combi boiler would be inadvisable and normal mains pressured showers will have poor flow.

For a 4 storey block of flats, it is unlikely that the 4th storey and above will receive any water with a mains pressure of 1bar. It should also be noted that the pressure at the mains stop tap will vary during peak demand periods of the day. Lower pressures occur in the morning and evening when everybody wants a shower or bath.

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