Paint with water was (and possibly still is) a basic coloring book with dotted or crosshatched patterns of dried water color paint inside of the area to be "colored."

The basic principle behind this was that kids could paint, without using actual paint (and hence supposedly avoiding a mess). The books came with a cheap plastic paintbrush taped to the inside cover.

My sisters and I would use the pages we didn't like as palettes to paint outside of the lines on the cooler pages.