You hear your Dive Rutland Staff members regularly asking you, and gently reminding you that you need to drink water.​We explain why but do you really understand dehydration and its relation to diving?


The body is 40 to 75 percent water and we need to maintain a relatively constant amount of water in the body.  Some urine must be produced to eliminate the nitrogen waste from metabolizing the protein in our food.  Therefore, eating a high protein diet will increase the amount of urine that must be produced and predispose you to dehydration.

The easiest way to determine your state of hydration is to observe the colour of your urine.  Dark yellow/orange urine means that your kidneys are trying to conserve water and are concentrating the urine as much as possible.  This means you are dehydrated.  Very light yellow or clear urine means that your kidneys are eliminating excess water from the body and that you are well hydrated.  At the same time, if you’re producing only a small volume of urine you’re dehydrated; if you’re producing a lot of urine you’re well hydrated.  These generalizations are usually true but there are a few medical situations where they do not apply.

If you are chronically dehydrated and producing concentrated urine you increase your risk of forming kidney stones and your risk of developing urinary tract infections.  Therefore, everyone should attempt to stay well hydrated and produce large volumes of dilute urine.  Drinking two litres of water daily (in addition to whatever else you drink) will achieve this goal in most people in temperate climates.

What is Dehydration?

Dehydration occurs when your body loses more fluid than it takes in, and this can lead to medical problems that should be and can be avoided.  For you as a diver there is another concern, dehydration is a major risk factor for Decompression Sickness (DCS).

Remember your Open Water theory training, where dehydration and contributing risk factors for Decompression Sickness are discussed.

Dehydration reduces the volume of blood plasma and perfusion of tissues, so it thickens the blood and reduces blood flow.  Since blood is partially responsible for the transportation of nutrients and for gas exchange, thickened blood will affect the off-gassing and Nitrogen and increase the risk of developing DCS.

What is Gas Exchange?

In secondary school, we learn that gas exchange is the process that occurs in our lungs, taking oxygen from the air that we breathe in and transferring it to the blood to go in to tissues for respiration and returns the carbon dioxide to our lung to exhale. As divers, we worry about nitrogen as well as we absorb more in to our tissues at depth, we need to make sure that it is carried to the lungs for exhaling as we ascend, remember your ascent rates and safety stops?

What is off-gassing?

As we descend, the increased ambient pressure causes more gas to dissolve in to our tissues, much like carbon dioxide is dissolved in to a fizzy drink. As we ascend, the ambient pressure drops and the gas comes out of solution, just like when you open the fizzy drink bottle. If we ascend too quickly, we cannot breath this excess gas off fast enough, and if our blood volume and blood chemistry is off balance, we cannot exchange the gas quickly enough. This increases the risk of decompression sickness which can happen to any diver, on any dive, even if there is no 'issue' with the dive.

What are the contributing factors to dehydration?

There are a number of contributing factors to dehydration :-

Breathing Compressed Air

The air in you cylinder has been through a number of filters whose job is to remove all of the moisture out of the air prior to being compressed into the cylinder. Water in a cylinder is a cause of rust and thats not something you want to breathe now is it?

This makes the air in your diving cylinder potentially very dry and as such 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 your moisture loss.

Immersion Diuresis (increased urine production)

During the dive the increased ambient pressure and cooler water temperatures 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


If you are already in a warm climate and sweating wearing just a t-shirt image how much you will sweat under your dive suit.  This also happens in the UK you know... wearing a drysuit and a thermal base layer does make you sweat, hence your first layer should be an anti-wicking layer.

Sun, Warmth and Wind

On a warm, sunny or humid day you sweat more.  If lost fluids are not replaced you become dehydrated.  Also the nice breeze of the wind evaporates sweat and moisture again increasing dehydration

Sea Water / Salt

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


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


Drinking alcohol and diving is never recommended, alcohol dehydrates you faster.

Sickness / Diarrhoea

Vomiting (e.g seasickness) or travellers' diarrhoea can dehydrate you, as large amounts of fluids and electrolytes are lost in a short period of time.


As in your dive cylinder the air in the cabin of a plane is much drier, causing your body to lose fluids faster.  Perhaps you are served coffee, cake or beer during your flight, but these liquids just don't have the same hydrating effect as water (as they are diuretics).  As a result, you could arrive at your destination with mild dehydration.  It is recommended to drink 240ml of water each hour of your flight.

As divers we like to dive daily and even several times a day, particularly if away for the weekend diving or on a diving holiday and as such we can understand the increased dehydration and DCS risk.

Signs and Symptons of Dehydration

Mild-Moderate  - easily resolved by drinking water

  • Thirst - drink before you are thirsty as thirst already means you are dehydrated a bit
  • Dry or Sticky mouth - When your body is low on water, it begins to pull water from auxiliary functions – such as saliva – to keep vital functions, such as consciousness, going. If your mouth feels dry and / or sticky, you are most likely dehydrated. 
  • Dizziness
  • Headache​
  • Muscle Cramps
  • Low blood pressure – Low blood pressure is a major indicator of dehydration, particularly if your blood pressure drops when you stand up immediately after sitting or lying down. Dizziness can occur as a result. 

Severe - immediate medical care is required

  • Extreme thirst and very dry mouth
  • Dry skin that sags slowly into position when pinched up
  • Rapid heartbeat, weak pulse - When blood flow is reduced due to dehydration, the heart begins to beat faster to keep what’s left circulating through the body. If your heart rate is elevated and stays that way, you could be dehydrated. 
  • ​Rapid Breathing

Preventing Dehydration

  • Keep your dive suit off until right before the dive itself
  • Protect yourself from to much sun / sunburn
  • Avoid alcohol
  • Rinse yourself down with fresh water after every sea dive

The best and easiest thing to do is to drink a glass of water every 15-20 minutes.  This will allow your tissues to be hydrated and consequently avoid the decreased gas exchange which can lead to bubble formation and DCS

Remember after EVERY dive you will be dehydrated so you need to drink and that includes the pool.. no excuse not to have water at any of our dive sites.. Remember the Dive Rutland water bottles, so no need for plastic water bottles and as a Refill station you can fill your water bottle whenever you are on site or passing.


v1.00 March 2019 - Club Newsletter