Here is a link to a great source for free topo maps.
caltopo

As for how much water, I can only tell you how much I bring. I live in the dry west. I can usually find a source by looking at the map. Once I went into some pretty dry mountains during a drought. I had to search out all the springs to find any water at all. I carried 2 liters with me. Normally I carry 1 liter, with an empty bottle to be able to carry 2 if I had to.
_________________________
I've taken a vow of poverty. To annoy me, send money.