This thread reminded me of an old thread about a expensive stolen stroller, fellow posters offered ways to make it too, icky to want to touch the new stroller. It started with the idea of using a new diaper but rolling it and taping it like a dirty one. Then it progessed to A clear plastic bag to hang from the handle, and a diaper soaked with a brown drink, to adding stuff, then hung in the plastic bag from the stroller handle. I'm not sure if this was just venting or for practical usage.
But if he's worried about the water you could use a couple of clean diapers to ward off any would be swipper of water bottles. It would make them think twice!!