St. Augustine will hold up rather well to pool water. Only (always a catch) do not let the water drain in just one spot, try to distribute the water around the yard. The worse case scenario you'll end up with a pretty nasty fungus in that one area. I have St. Augustine on two sides of my deck and from the water being splashed out, the sod around the deck gets a nasty fungus that will turn the blades of grass a rather odd shade of orange.