Before she joined the crew of the spaceship Voyager, the Ocampa Kes was living on a desert planet.
Once the planet was green and lovely but an experiment of an god-like alien went wrong and turned the planet surface into a desert.
The god-like alien-creature rescued one of the two species who lived on the planet. It brought the species of the Ocampa into the caves of the planet where they could live in peace and allways had enough water. But it didn't care about the other species on the planet: the Kazon. The god-like alien closed the caves with an energy field, so the Kazon weren't able to reach the water.
One day the young Ocampa female Kes got bored in the caves and sneaked out of them although it was against the law. On the surface of the planet she was captured by the Kazon. Her way back in the caves was blocked by the energy field. Some months later she is rescued by the crew of the spaceship Voyager and becomes part of the crew.

The US-series of course never told the viewer in detail, but it's pretty obvious that during these months Kes probably got assfucked twenty times a day by the very pissed-off Kazon to earn the water she needed to survive...and then she got a nice boyfriend...