I think cats will naturally pee/poo in water.
This is going to sound really disgusting, but, we keep our litter tray in the bathroom, one night, the bathroom door got knocked shut (prob by the cats), so they couldn't get to their tray.
I had left a washing up bowl in the kitchen sink and it was about 1/3 full of water, when I got up in the morning, I found several cat poos floating in it. I thought it was very strange! There was at least 3 cats worth of poo in it (I had 3 cats at the time), so they all had the same idea, plus my cats almost never jump on the kitchen side, so I don't even know how they thought of it.

By the way, I threw the washing up bowl out and disinfected my kitchen alot!
But I must say, I was happy that they didn't poo on the cream carpet or anything like that!