Ruby will dig in water bowls when she feels the need to play. She likes the movement on her feet and she likes to "bite" the wake for fun... she also dunks her face in water up to her eyes and then runs around. Overall, I think that she enjoys playing with it after she's gulped her fill.
She also lives with a Lab, and has determined that getting in the lake with Allie is now a necessity. So to her, water is a plaything, anytime, anywhere, no matter who the bowl belongs to, LOL.
I might add that I live in Iowa, so during the summer it gets disgustingly hot and humid. We have a plastic little pool, and when the girls go outside during the summer, if it's really hot, Ruby will lay down in the water to cool her belly. So I think that digging at water sources could be for fun and to cool off. Just be glad that she's digging at water bowls and not in the yard LOL.