Survival Day

In Dark Sun, the wild is unforgiving, and in order to survive outside the cities, one must be prepared. In order to make the rules simple, it is assumed that in order to survive normal conditions in the wild for one day, that you need to have several things at hand. These things are called a "Survival Day" worth, and include: clothes to protect from the sun at night, clothes to protect you against the cold at night, food to eat, water to drink and different salves to protect the skin against the merciless sun.

This means that forcing beggars to give up their water won't make it up for a "Survival Day", only a small part of it.

It is possible to forage in Athas, if you have run out of water and/or food, but it's very difficult.

In game terms: As long as you expend a Survival Day while in the wilderness, you are (under normal circumstances) protected from Sun Sickness, which is the most common affliction that you suffer when out in the sun.

Sun Sickness, once acquired, can kill you in as little as two days. Traveling in Athas is dangerous, there is no mercy nor help to get from the world itself.