It depends. Many will say no problem at all, and some others see the grass go brown. I suspect a variety of things influence that reaction like the type of grass, soil type and hydration, pool water chemistry, etc. If you're not in a hurry, you can always pour some pool water in a test area for a day or two and see what happens. Might take about a week before you really know or not.is it safe to drain pool water onto the grass?