"Water view" is a specific room category at POFQ (and in fact, at all 4 Moderate resorts) that costs extra per night. People can certainly REQUEST water view, but they must realize that by requesting it, they are asking for a free upgrade.
If you RESERVE and pay for a water view room, you are guaranteed a water view room. What is NOT guaranteed, however, is what sort of water you will be viewing. It could be the Sassagoula River, or it could be the pool (as noted in posts above). There is NO WAY to guarantee one or the other ... it is purely a matter of request, and then a matter of luck.
And this is the same at the other Moderates, as well.