It will rarely be necessary to switch the mains water supply off where it enters your plot, but it is wise to know where the stopcock is, just in case.
Anaml iawn y bydd angen diffodd y brif bibell ddŵr yn y man lle mae'n dod ar eich safle, ond mae'n ddoeth gwybod ble mae'r stopfalf, rhag ofn.