Dune (novel)
Arrakis is a planet that is almost covered in desert. This large desert is very dangerous because it does not have potable (drinkable) water, but mainly because giant worms live in the sand. There are many groups of native humans living there - they are called the Fremen. The Fremen have many rituals that keep water safe. This is important, or they would all die of dehydration (too little water to stay alive).