No matter what I do I can't seem to keep fresh clean water in the ducks bowls. I have four ducks and they have three metal dog bowls filled each morning with clean water. Within about 10 seconds it is filthy again, and if I leave them they end up just full of mud. I have tried these plastic drinkers and they are exactly the same. At the moment the duck run is just earthen with some type 1 hardcore to prevent it getting too slippy, but I need to put some other ground cover in there - suggestions are sharp sand and wood chips/bark. Should I worry about it or just fill the bowls when I see them getting bad. If I'm out for the day they would just have to stay that way anyway. Any thoughts?