To hydrate means to add water to something or to drink enough water to keep your body working properly. When you hydrate after playing soccer on a hot day, you're replacing the water your body lost through sweat. Athletes hydrate before, during, and after games to stay strong and focused.

Your body needs water for everything: thinking clearly, keeping cool, moving your muscles, and digesting food. When you don't drink enough, you become dehydrated, which can make you feel tired, dizzy, or give you headaches. Signs of dehydration include dark yellow urine, dry mouth, and feeling thirsty.

The word also works in other contexts. Scientists hydrate dried-out samples in labs by adding water to them. Hikers carry water to stay hydrated on long trails. Some people say “stay hydrated!” as a friendly reminder to drink water, especially on hot days or during exercise.

The opposite is dehydrate, which means to remove water from something. Beef jerky and raisins are dehydrated foods: all the water has been taken out so they last longer without spoiling. Your body can also become dehydrated if you don't drink enough water to replace what you lose naturally every day.