In Australia to have one you are supposed to have an RPZD fitted and annual inspections by a licensed plumber which isn’t cheap. But you can go down to bunnings and get a hand spray with a t piece that comes off the stop cock for your toilet. But a plumber won’t install it for you.

It’s to do with not having shit go back into the water system. There’s also some worry about the hand sprays falling in the bowl and causing bacterial growth. This may all be different in other states though.