Burst pipes, sewage overflow, gas smell (call the gas network first), no water, or a collapsing ceiling from a leak. Shut off the water at the meter while you wait.
Yes - nights, weekends and public holidays typically carry a call-out premium. For non-urgent jobs, booking standard hours saves the surcharge.
Only minor tasks like changing washers. Work on pipes, drains or hot water systems must be done by a licensed plumber, and may need a compliance certificate.
Turn the main tap at the water meter clockwise to shut off supply, open the lowest tap to drain pressure, and switch off the hot water system.