Can this valve be used for water?
It is common/normal for valves to be rated for multiple service types.

As such, so long as it is rated/certified/locally acceptable for the type of service it is in, and rated at or above the operating service pressure of the service it's in, it's fine.

Locally, I'd be looking for a "NSF-PW" (National Sanitation Foundation - Potable Water) or one of a number of other more obscure codes indicating suitability for potable water service. 

If it can also handle gas, I don't care, in water service. In gas service, I care that it can handle gas, and is suitably rated for that service, and I don't care what the water ratings (if any) are. The only place I might care about both would be my spare parts collection, where one valve could fix either type of service, if suitably rated for both.

If it makes you happier, paint the handle blue, or red, or whatever color you expect it to be.