I had a fun thought. Namely, things that are good for dessert aren't good for desert. And vice-versa. Dessert is usually sweet or at least with a strong taste, that would in practicality only make you more thirsty.
Alternatively things that are good for the desert, like water and good food, wouldn't be good for dessert.
However, I actually have no idea about desert life, making this post rather redundant. Still... It was a fun thought.