After roughly the first four floors in a building, mains pressure water will typically be no longer suitable to move water around. Instead, water is pumped to the tank on your roof.
In theory, the tank then supplies most remaining floors via gravity - except for the four or so floors directly underneath it, where gravity would not provide sufficient water pressure, which need to be supplied with water from a pressure-boosted system via a pump.
In practice, many buildings with central water tanks do not have separate plumbing lines for the top floors, and all water used in the building is pumped from the tank. You’ll need to check your hydraulic diagrams to ascertain exactly how water moves around your building.
This means that every drop of water is pumped from ground level to the tank, and then from the tank to where it is used.
Options to consider in ensuring efficient operation of your building’s water supply are:
- Pressure boosting the water supply lines out of the roof tank is common, though it is only necessary for the top few levels. Well-specified pumps with ‘pressure modules’ will help to limit energy used by these units.