There's nothing wrong with extra water coming in. The concern with runoff is the stuff that comes with it. It's a quick and easy way to pollute your pond. Anything in the waterfall, however, will be fine; it's my favorite way to fill my pond!It rained pretty hard today and I didn't really see any specific trouble spots. I really thin we are going to ne okay in this department other than the fact that once the fall has epdm under it and runs into the pond it mightadd to the water level so I do still feel the need for a garden overflow.