Kathy, It is not necessary to waterproof. If I remember, you're working with topping mix. It will hold water. Billie

Thanks Billie, You remember correctly but I switch back and forth. Sorry I didn't give you all the information. Some day I will figure out that you can't read my mind. It's probably a good thing you can't for your sake! Many days it seems to be empty and the rest is dangerous. You are probably praying that I will go away. Seriously I do appreciate all your help. The birdbath/water receptacles are turfa. With no holes they tend to hold water for awhile tho. Kathy