Nine factors that play a major role in a scuba diver’s dehydration

Dehydration occurs when your body loses more fluid than is taken in, and this can lead to medical problems that should be avoided. For you as a diver there is another concern: dehydration is a contributing risk factor for decompression sickness (DCS). Why? Dehydration reduces the volume of blood plasma and perfusion of tissues, so it thickens the blood and reduces blood flow.
Nine behavioural and environmental factors play a major role in the diver’s dehydration:

1. Breathing compressed air: The air in your scuba cylinders is dry and you lose more fluid to humidify this dry air. Due to the colder water temperature, your lungs need to work even more to warm up the air and this increases the moisture loss.
 
2. Immersion diuresis (increased urine production): During the dive the increased ambient pressure and cooler water temperature causes the blood vessels in the extremities to narrow and blood is shunted from the extremities to the core of your body (heart, lungs and large internal blood vessels) in an effort to keep you warm. As a reaction the kidneys produce more urine, which means losing water and salt again.

3. Sweating: If you are already in a warm climate and sweating wearing just a t-shirt, imagine how much you will sweat under the dive suit.

4. Sun, warmth and wind: On warm, sunny or humid days you sweat more. If lost fluids are not replaced, you become dehydrated. Also, the nice breeze of the wind evaporates sweat and moisture, increasing dehydration.

5. Seawater/salt: When salty water dries on your skin, it leaves salt crystals behind. This will take the moisture out of the skin, increasing dehydration further.

6. Medication: Some medication may have diuretic effects. This means they increase  dehydration as they actually absorb water out of your body cells and increase urine production.

7. Alcohol: Drinking and diving is never recommended; in addition, alcohol dehydrates you faster.

8. Sickness/diarrhoea: Vomiting (e.g. seasickness) or traveller’s diarrhoea can dehydrate you, as large amounts of fluids and electrolytes are lost in a short period of time.

9. Flight/airplane: As in a diver’s cylinder, the air in the cabin is much dryer, causing your body to lose fluids faster. Perhaps you are served coffee, coke or beer during your flight, but these liquids just do not have the same hydrating effect as water (they are diuretics). As a result, you could arrive at your destination with mild dehydration. It is recommended to drink 240 ml of water each hour of the flight.

Considering that many divers like to dive daily and even several times a day, for example on  weekends or on a diving holiday, then we can understand the increased dehydration and DCS risk.