The Key to Proper Hydration in Technical Diving

By Leo Fielding

Proper hydration is essential for technical diving. Your body weight is nearly two-thirds water. However, all too often, divers drink too little, too late or drink fluids that don’t hydrate them properly. Many divers also don’t consider drinking water once a dive is underway.

Leading technical divers have long known the importance of proper hydration. For example, the divers who undertook the Britannic dives in Greece in the early 2000s not only continued to hydrate right up until the point of water entry but also during decompression. Ditto to the British cave divers who explored the deep submerged caves of northern Europe in the 1990s.

Given the importance of proper hydration, here are three ways to keep your water levels up:

  • Recognize what dehydrates you
  • Hydrate properly before a dive
  • Consider drinking water during the dive

Above: Divers with a water container to hydrate in-water during the 2003 Britannic expedition dives. Photo Leigh Bishop 2003.

Recognize What Dehydrates You

While divers are drawn to water, many go through life in a constant state of dehydration.

To properly manage dehydration, we need to recognize its causes. The causes are simple: sweating, urinating and breathing. Even before you board a dive boat, it’s easy to get off to a bad start. Caffeine and alcohol stop the body from releasing the antidiuretic hormone, which makes you urinate more. Air travel makes you lose water vapor through breathing because your lungs have to humidify dry cabin air.

On the boat and in the water, there are many risk factors specific to diving itself that may exacerbate dehydration. These include:

  • Environmental factors: technical diving from boats can involve long journeys out to offshore sites and so can present challenges for proper hydration. Kitting up in thermal undersuits makes you sweat. Wind and sun evaporate the water on your skin. Salt water will dry and leave salt crystals on your skin, which in turn absorb moisture. Seasickness can cause vomiting and fluid loss.
  • Immersion diuresis: diving involves increased ambient pressure and cooler water temperature. As a result, the body shunts blood from your extremities to your core to try to keep you warm. Our bodies interpret the increased blood volume in our core as excess fluid. In response the kidneys produce more urine: the rate of fluid loss is fast at first, then slows over time. According to the US Navy Diver’s Handbook, simply being underwater for an hour may cause a diver to lose 0.25-0.5 liters/9-18 oz of fluid.
  • Breathing dry gas: open-circuit (O/C) divers breathe dry gas. The same goes for divers who have had to bail out onto open-circuit from a closed-circuit rebreather (CCR). They humidify that gas in the mouth and throat and then exhale humid gas. This means the body is constantly losing fluids just from breathing. This is less of an issue on a CCR, where the diver breathes a humid gas that is recirculated around the loop.

Dives involving substantial deco further exacerbate these factors. This is because of the activity levels and the run times involved. The more we do and the longer we do it, the more our bodies are affected. Carting around bail-out cylinders, scooters, lighting and video equipment all takes its toll. The longer the runtime, the greater the fluid loss through sweat (physical activity), urination (immersion diuresis) and breathing (humidifying dry gas).

Researchers have found that pre-dive hydration significantly decreases bubble formation after decompression, thus offering a relatively easy means of reducing the risk of decompression sickness. One hypothesis is that proper hydration helps maintain the volume and flow of blood around the body, which in turn is key to gas exchange. However, as is the case with many aspects of decompression theory, there is much we still do not understand.

Hydrate properly before a dive

Above: Divers preparing to dive Britannic at 120 m during the 2003 expedition continue to hydrate right up until the point of water entry. Photo Leigh Bishop 2003.

Happily for technical divers, proper pre-dive hydration is relatively straightforward. Here are some tips:

  • When to drink? Starting at least 24 hours before a dive is sensible. Do not wait to be thirsty before drinking. If you are thirsty, chances are you are very dehydrated.
  • What to drink? Water is sufficient for mild dehydration. Fruit juice is better than nothing, but not as effective as water. Isotonic or “sports” drinks are widely considered unnecessary: diving itself is not thought to generate enough electrolyte loss to worry about. The exception to the rule is hot climates and/or involvement in pre or post-dive exercise, where additional electrolyte replacement may be needed.
  • How much? What works for me is the advice in the TDI Advanced Trimix manual by Steve Lewis: “at least three liters a day for four days before diving and increasing that by 50 percent on dive days” and checking urine to avoid “anything darker than a light straw colour”. Remember water intake needs vary by individual, activity level, climate, and so on. Proper hydration does not mean excessive hydration.
  • What if I need to urinate? Proper hydration presents challenges to drysuit divers. If you do not already have a pee valve or a snazzy pair of incontinence pants, now is the time to acquire them. Never be tempted to limit your fluid intake before a dive to avoid needing to urinate!

Above: The wreck of the Numidia (80 m / 260 ft) in Egypt. Diving in hot climates may require additional electrolyte replacement. Photo Leo Fielding 2018.

Consider drinking during the dive

Drinking during exercise is the norm in many sports. On really long dives, proper hydration doesn’t stop once you hit the water. This is when technical divers turn to in-water hydration. Is this a challenging skill? You bet. Can it be learned with practice under the right conditions? Sure it can. Common choices include:

  • Hydration reservoirs available from outdoor activity stores
  • Pouches of fruit juice

A reservoir or pouch can be stowed in a dry suit pocket. They come with bite-valves or screw lids. Either works fine.

  • Bite-valves may be simplest if you’re wearing gloves, as you won’t need to use your hands to open and close the container. Many bite-valves also self-seal after each sip.
  • For screw lids, place a finger over the lid, remove your reg with the other hand, squeeze and drink! Small sips work best. When you’re done drinking, replace your finger, replace your reg and signal okay.

Some CCR divers go directly from breathing on the loop to the drink, others bail-out as an intermediate step. Like with any skill, work into a rhythm and relax.

A good time to rehydrate is on the shallow stops. As shallow stops tends to be the longer stops in an ascent, they allow time to sort yourself out with a drink. And given shallow stops come towards the end of the dive, this is the time when your fluids are likely to be most in need of a top up.

On dives requiring support divers, the support team may fasten CamelBak-style reservoirs to a deco station, as was done on the Lusitania and Britannic dives of the 1990s by the Starfish Enterprise team, or to the inside of a habitat.

Above: A wide range of hydration reservoirs are available from outdoor activity stores. If you must use a disposable container, remember to take any litter with you!

Before you try in-water hydration on a dive involving substantial deco, practice with a buddy in conditions that are well within your comfort zone using a stable platform and a visual reference. With practice, you should be able to execute this skill while maintaining your position in the water column. This is not a skill to be attempted for the very first time off Malin Head in a 2 m /6 ft swell with hours of deco ahead of you.

The saying goes that you can lead a horse to water, but you can’t make it drink. Let’s ensure the same isn’t said about technical divers.

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3 replies
  1. Fred
    Fred says:

    Good article but since one the goal of these articles is to inform, I would like to comment and help inform.

    1. “Air travel makes you lose water vapour through breathing because your lungs have to humidify dry cabin air “(second paragraph under the section Recognize What Dehydrates you). We ALWAYS release water vapour when we exhale; not only when we are inside airplanes or other low-humidity environments.

    2. “Diving itself is not thought to generate enough electrolyte loss to worry about.” If you sweat (as mentioned by the article) you do lose electrolytes; in long and demanding dives (especially the ones where deco is lengthy), people do urinate. Therefore, the author mentions sweating and long decos as increased risk factor for dehydration but later on says “Diving itself is not thought to generate enough electrolyte loss to worry about.” I agree that when I dive in Cozumel, staying underwater for 1hr or 1:20hr each dive is not enough to lead to severe dehydration so Gatorade or Pedialyte are not a necessity. But what type of diving is the author addressing?? Rec (1-tank OC, shallow, no deco) or Tec (rebreather/multi stage, deep, long deco)? 3mm wetsuit or drysuit with heavy/thick undergarments? He constantly talks about highly Tec and demanding dives. Therefore, the physiological demands are completely different and Gatorade (which also has glucose added) and Pedialyte are definitely better choices for rehydration.

    Also, dehydration is not only loss of fluids. Loss of electrolytes (minerals), even when drinking plenty of water, leads to changes in the osmotic balance of tissues (not enough electrolytes in the blood and tissues) and may culminate in hyponatremia – a condition that may cause brain swelling, unconsciousness, coma, and death. Just google “woman dies mall drinking” and read about hyponatremia.

  2. Brock Brinkerhoff
    Brock Brinkerhoff says:

    The dangers of overhydration should also be considered. During two recent Navy studies performed at Duke University (of which I was a participant in both), the research focused on hydration and its impact on immersed pulmonary edemas. The initial study dealt with pulmonary pressures and attempted reductions of those pressures. The second focused on hydration and overhydration. Both studies were done while fully immersed and breathing on a ccr loop performing exercise. The overhydration study showed the correlation between hydration (specifically overhydration) and the onset of a pulmonary edema. I personally showed signs of a developing pulmonary edema during the overhydration test, and the testing had to be stopped.

    As with most things, there’s a balance.

  3. Glenn
    Glenn says:

    The key is the second most important invention for diving after the demand valve… the Pee Valve. Having one of those fitted to your drysuit ends the pre-dive drinking embargo. These are especially important for longer dives or the ‘older’ diver. This means you can now drink tea and coffee before a dive and ensure you’re properly hydrated. Not only is this vital for decompression; it’s vital for comfort too.

    To illustrate this, I recently went on a week-long recreational diving trip in Scotland. My drysuit zip broke on the first day so I had to hire a drysuit which didn’t have a Pee Valve. It was horrible having to jump in without being sufficiently hydrated and having that constant ‘I need a pee’ feeling. Whilst the dives were all short 60 minute dives, I did have to shorten one dive and was rather quick at de-kitting. Really not a nice experience.


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