This crew's water and food bowls get washed at least once daily - even if they look clean. I know that plastic ones aren't the best choice, so that makes washing thoroughly even more important. With 5 cats and a dog all in the house, I always make sure that they have fresh, clean water, since everyone drinks from whatever bowl they feel like. There are 2 big plastic ones in the kitchen, 2 stainless ones in the family room, and a plastic and a ceramic for Wolfy in my bedroom. Of course the cats like Wolfy's, and Wolfy likes the ones in the kitchen - go figure!!