Fitting an external tap at a commercial premise

[Malcolm Greenhouse]

I have been asked to fit an external tap at a mental health facility to enable the external paths to be hosed down. What form of back syphoning measure is sufficient for this installation?

 

[Ric2013]

It's a very weird one actually. Because the tap itself has no backflow potential unless we already know what it is likely to be used for (which we do). Similarly, you could theoretically fit a washing machine valve with 3/4" thread without even a SCV in line (assuming the washing machine IOM states that no backflow protection is required - I always fit a SCV as I doubt any customer will ever bother to check) and then the customer could later connect a garden hose and use it to unblock the kitchen sink (cat 5).

IIRC if the hose union bib tap were internal (rather than external) to a domestic premises and perhaps used to fill a mop bucket, you could quite legally fit it without any backflow protection at all. Then, if a hose were attached, the need for a DCV arises as the hose is a new installation.