Dehydration occurs when you lose more fluids than you take in. Dehydration is not a serious problem in normal case. But if you lose large amounts of water you may feel quite sick. Dehydration occurs due to various reasons. It is true that gastrointestinal illness may cause dehydration as you may lose fluid through vomiting and diarrhea. Those who work outside should replace fluid lose through sweating and urination as otherwise they may get dehydrated. The best solution for dehydration is fluid replacement. Many people with dehydration problem may require intravenous fluid application. It all depends on the assessment of the extent of dehydration. You should take plenty of fluids and eat foods high in water such as fruits and vegetables to reduce the risk of dehydration. You should give more water if a person is having illness as you should not wait until dehydration occurs. If you do regular exercise, you should see that enough water is consumed before and after doing exercise.