This is a useful guide to the subject, since it deals with the need to have water storage when you actually have a city water supply.
That sounds strange, but in South Africa it happens.
It gives insight even for Rainfall collection schemes.
The whole site has good insight to plumbing a home.
backup-water-large-home/
'A backup water system stores municipal water in a tank on your property and uses a pressure pump to feed your plumbing when supply is interrupted.
A typical system consists of the storage tank, a pump with pressure control, a filter to protect the pump, and the plumbing that connects it to either your whole house or selected outlets. hen municipal supply runs, the tank quietly refills; when it stops, your taps keep working from storage.'
Calculating Peak Simultaneous Demand
Installers typically assign a flow rate to each fixture type — showers, basins, toilets, kitchen taps and outdoor taps — and then estimate how many are realistically open at the same time.
For a large home, a conservative working assumption might be:
- Three showers running together
- One basin tap
- One toilet cistern refilling
- One kitchen tap
Adding those flows together gives a peak demand figure in litres per minute (l/min). The pump must comfortably exceed that figure at the working pressure your home requires — typically around 2.5 to 3.5 bar for normal domestic fittings.
Pipework diameter matters here too. Undersized pipes create friction losses that choke flow regardless of pump power.
A good installer calculates the pressure drop across the full pipe run, not just the pump spec sheet.
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