The supply of water into your house may be one of two distinct types. So that you are able to deal correctly with an emergency, or to make changes to your system, it is a good idea to check out which you have.
In this set up, mains water is supplied directly to all taps and WCs. This tends to be the system used in older houses.
The indirect system is the commonest form of water supply into modern houses. The mains water is supplied directly to the kitchen sink (and sometimes to an outside tap).
All other water supply is via a storage cistern. The mains water comes into the house, branches off to supply the kitchen, and rises to the storage cistern.
From here, the other appliances are fed under gravity pressure caused by the height of this cistern above them.