Effects of Dehydration on the Body

Water helps maintain blood volume and carries nutrients and waste. With too little fluid, you may feel thirsty, light-headed, tired or headachy. The kidneys conserve water, so urine often becomes darker and less frequent. The mouth and skin may feel dry, while concentrated urine can irritate the urinary system.

The body also relies on sweating to release heat. Dehydration during hot weather or exercise can therefore make overheating more likely. Fluid loss from gastroenteritis may combine vomiting and diarrhoea, making replacement harder. In some people, reduced bowel water contributes to constipation.

Drink small, regular amounts rather than forcing a large volume at once. Oral rehydration therapy is useful when vomiting or diarrhoea has caused loss of both water and salts. Move to a cool area, rest and replace clothing dampened by sweat. Continue checking whether you are passing urine and whether it is becoming lighter.

People with heart, kidney or liver conditions may need individual fluid advice. Ask a clinician before making a large change to your intake, especially if you use medicines that alter urination.

Seek urgent help for fainting, confusion, severe drowsiness, inability to drink, repeated vomiting, or little to no urine. Severe dizziness when standing, a racing heartbeat or signs of heat illness should also be assessed promptly.

Contact a clinician if fluid loss continues or symptoms do not improve after drinking. Persistent dark urine, cloudy urine, pain or fever may point to another problem as well as dehydration.

How much fluid is appropriate for my health conditions? Do I need oral rehydration therapy? Could my symptoms be caused by infection, heat exposure or a medicine?