I want to fit an electrically operated valve on the mains water pipe to my home.
When the power supply to the valve is on and live the valve is open and allows water to pass to my home.
Whem I manually switch the power supply "off" to the valve I want the valve to close and not allow the water to pass through the valve to my home.
Is this described as a normally open valve.

Can anybody recommend such a valve by manufacturers type, I believe there could be about 12 bar pressure in the water pipe.

Regards Pajoken

What you want is a normally closed valve. That means that it is closed unless electrical current is present. That valve would probably employ a normally open relay but the valve itself would be normally closed. Valve would probably be low voltage, therefore require a low voltage transformer

Google "electrically controlled water valves"

Probably can be found locally at heating supply business.