[briteday]

Protein, per se, does not cause excess water to be eliminated through the kidneys. However, it does cause the kidneys a bit of extra work to process. So drinking more fluids would be helpful. Drinking more fluids would dilute the protein in the blood, making it easier for the kidneys to process the protein present.

[wyx]

I think the "too much protein" thing is pet feed manufacturer propaganda, to make people think they need to feed their dogs more carbohydrate, which has higher profit margins than quality protein and fat sources. A diet high in carbohydrate will destroy your pet's kidneys down the line due to diabetes, if they don't die from cancer or heart disease first (also caused by high-carb diets).