Actually, nuclear powered carriers and subs don't have a water shortage problem - they've got lots of fresh water all the time, courtesy of nuclear power and desalination equipment. Destroyers and cruisers both do OK in the water department. It's only amphibious ships that can have a problem, and then only when they're carrying a full load marines. But there are many discomforts of living on an amphibious ship, and taking more frequent showers ranks rather far down on the list.
Talk about pissing away our defense dollars. Citing a non-existent water shortage aboard U.S. Navy ships, Congress wants the navy to spend $2 million to have a Michigan company adapt its "water-free" urinals for ship board use. To add insult to injury, Congress wants the navy to take the money from its operations (ships at sea for training) and maintenance (keeping the ships in good shape) money. This, unfortunately, is so typical of how Congress uses the defense budget to take care of their friends and supporters, at the expense of the troops.