Do you Need a Non-Return Valve on the Shower Hose Wall Outlet?

[Scorps79]

I am purchasing a hand shower on a rail
and have a choice for the wall outlet -
this can either be with or without a
non-return valve.

Is it better to have the non-return valve,
if so, why ? because it is more expensive.
Also one has a pivot joint and other does
not so I do not know if this is important.


Thank you in advance for any help with this.

 

[lame plumber]

if the shower head reaches the water level in a bath/shower you need a non return valve building regs and water regs require it to stop you possibly polluting the water main

 

[JCplumb]

If you install the shower and it has one of those rings on the riser that you put the hose through and once through the ring it cannot drop to the level of the water can you skip the NRV?
I've always thought so, but I have been wrong about such things on the odd occasion :/
I mean potentially, the customer could unscrew the shower head and take the hose out of the ring which would mean the head could drop to the water level...