Why do scientists talk of liquid water? I thought in it's liquid state it is just water, when frozen it is ice and when it evaporates it is gas.

While water is our common usage for liquid water, water, in a scientific usage, applies to the molecule H2O in any state. Thus solid ice is still water. Vapor is still water, and liquid is also water. Scientist use the state to specify what state of matter the water molecule is in.