Update: I added three new layers in an attempt to make water. The water layer is just a selected area filled with blue at normal and 75% opacity. I know water isn't "blue," its translucent and reflects whatever is above it, but... I didn't know what else to do there.
The top layer is just a 50-px brush around the edge, then a gaussian blur with a radius of 100 px.
The bottom later is the floor texture copied, then blurred by a radius of 5 px.
It just looks kinda... surreal. Not really like water, I don't think. Reducing the opacity of the blue makes it more translucent, but not really closer to water.