Dehydration

Dehydration is a medical condition in which a body experiences an excessive loss of water.

Symptoms
Common symptoms of dehydration include increased thirst and tiredness. In some humanoids (such as Arkonians), dehydration causes acute cellular breakdown which increases the risk of transporter accidents. 

Prevention
When in an environment conducive to dehydration (such as a desert), breathing through one's nose helps to prevent the body from losing too much water. Captain Jean-Luc Picard recommended this to Wesley Crusher when the pair crash-landed on the moon Lambda Paz. 

Treatment
Neodextramine solution is a medicine that can be used to treat dehydration. After Harry Kim was forced to return to the USS Voyager from Banea, he suffered from dehydration in his shuttle. Upon returning, he was given a neodextramine solution.