Princess is notorious for this & it started as a pup. I've heard it's to cool their paws since they sweat from their pads, which sounds right.
But she has learned to do it when she's mad if I'm ignoring her. She'll dig up the entire bowl while glaring at me. If I still don't respond she'll knock it over.
My parents have a deeper bowl for bigger dogs & she only drinks out of it with her front paws in it at the same time.
But she's usually pretty worked up there running around.
So there's a couple of possible reasons from our end.
