The main challenge with eating and drinking in space is that there is no gravity. If you let go of a piece of food in a space craft, it will drift around, not falling to the floor. Water will not stay in a cup, it will float out and hang in the air. Food crumbs may float around the spacecraft causing harm to astronauts or the equipments.
Many types of space food are dehydrated, or freeze-dried, and sealed. When the astronaut is ready to eat the space food, he can add water to rehydrate the meal so that it will be edible. Space food is provided in disposable containers that can be attached to the astronaut's meal tray, which is strapped to his lap, so that the containers do not float freely through space.
Astronauts expend a lot of energy and endure extreme stresses on their bodies. Their dietary requirements are therefore different from those of their gravity-bound counterparts on Earth. For example, they need extra calcium to compensate for bone loss.