In one of the books I've read about crusades there was a siege, where the people locked in a fortress were out of water while the weather was quite hot. So how

In one of the books I've read about crusades there was a siege, where the people locked in a fortress were out of water while the weather was quite hot. So how do you get water when totally desperate and thirsty? They immersed their leather belts in the cesspit, then after a while, pulled them out and squeezed the water out, plus, of course drank their own piss.