In many countries it is customary to have a bidet spray inside the bowl of the toilet, which is operated by an on/off isolator valve located conveniently to hand on the wall.
Having the bidet spray nozzle located within the toilet bowl has a number of benefits:
It keeps the water inside the bowl, thus reducing water splashing on the floor, which could be unpleasant for other users and a potential slipping hazard.
The inbuilt nozzle is more reliable than a handheld spray.
The inbuilt nozzle, unlike a handheld spray, cannot be stolen.
Back Flow Preventer
In some countries, including the UK, building regulations exist which stipulate that a back flow preventer is installed in line to the bidet nozzle, to avoid the possibility of germs flowing back to the main water supply.
