Drinking water when you work outside especially on hot days is important for kidney health. Water removes waste from your blood in the form of urine and helps to open your blood vessels so nutrients can reach your kidneys. When you are dehydrated, your kidneys have to work harder to remove waste and deliver nutrients. Mild dehydration causes fatigue and can impair some normal body functions. Severe dehydration can lead to kidney damage, so itâ€s important to drink enough when you work outside or exercise very hard, and especially in warm and humid weather. Frequent dehydration may lead to permanent kidney damage.