The purpose with a domestic water supply system is to provide the consumers with enough hot and cold water.
Common in old buildings is the system with gravity storage tanks on the top floor of the building. More common in new systems are pressurized tanks connected to the supply pumps.
The domestic water supply system with gravity tank is presented below:
For proper operation of the system, the gravity tank is located at least 30 ft or 10 m above the highest outlet or consumer. In tall buildings it's necessary to use pressure reducing valves in the lowest floors before the fittings.
The volume of the tank must be designed to compensate for the limited capacity of the supply lines. The tank fills up when the consumption of hot and cold water is lower than the capacity of the supply lines - and the tank is emptied when the consumption is higher than the supply lines capacity.
A drawback with the system with the open gravity tank on the top floor is the potential danger of freezing during winter conditions. Huge tanks will also influence the construction of the building.
The domestic water supply system with a pressurized tank is presented below:
The pressurized tank is partly filled with air behind a membrane. The air compensates for pressure variations during consumption and during supply pump starts and stops.
The pressurized tank has a limited compensating capacity for shortage in main supply lines.
You are free to use the template bellow as a tool to estimate required buffer capacity in a water supply system. Log in to your google account to make your own copy of the template. Alternatively - save the file as a spreadsheet to your computer.