​More Water Less Bubbles

​What is dehydration and how does it influence Diving safety? Dehydration is an abnormal state of relative loss of water due to either a reduction of water intake, an increased loss of fluid, or both. There are many causes for this and these may produce a range of dysfunctions from minor to major medical problems such as headaches, decreased physical performance, irritability, confusion, fatigue, muscle cramps, reduction of thermoregulation, and impaired consciousness. If sustained over long periods, chronic dehydration may lead to kidney stones; if severe, it may result in hypovolemic shock and death. As such, it is potentially harmful for divers and non-divers alike and should be actively prevented.

​​Divers have an additional concern, however: Dehydration is a significant risk factor for Decompression Sickness (DCS). In simple terms, dehydration reduces the transport of various substances in the blood, including the elimination of dissolved gas. If tissues suffer a loss of circulation or if the thickness (i.e., viscosity) of blood increases, effective gas exchange is impaired with a potential accumulation of nitrogen and an increased tendency for bubble formation and compounding circulatory disturbances if bubbles were to arise.

How big is the risk on DCS? Although exact figures are hard to come by, Dive Safety Laboratory (DSL) and Project Dive Safety (PDS) studies have indicated that some level of dehydration is present nearly universally amongst divers. It is also a frequently reported finding in those who eventually become symptomatic with DCS. The point is that diving increases the risk for dehydration and for DCS but this risk can be reduced readily and easily by means of active rehydration.

Why does the risk for dehydration increase during diving and dive trips?Obviously it is not the dive trip as such, but the associated factors that promote a state of gradual dehydration.

Diving Factors

Last, but not least, diving itself challenges our fluid stores. There are several reasons for this including:
  • Significant increases in perspiration while wearing thermal protection gear (e.g., a wet- or dry suit)
  • Salt-water exposure and wind-related evaporation of fluid
  • Immersion diuresis (i.e., the increase in urine production due to a shifting of body fluids in the gravity-reduced state of being in water), and
  • Breathing dehumidified compressed air, which causes additional respiratory loss of moisture. 

Non-Diving Factors

Increased physical activity, exposure to sun and heat, sun burn, exposure to salt water, and wind exposure all deplete the body’s water stores. Alcohol and caffeine intake compound these losses. Many divers also take blood pressure medication which includes diuretics. Finally, diarrhoeal illness, fever and vomiting due to food and water contamination or motion sickness – which are all common on dive expeditions – may all aggravate the state of dehydration. 


Travel contributes significantly to dehydration: Access to water is restricted and certain methods of travel – such as flying – not only impose physical restrictions on carrying liquids but also increase the loss of fluids due to the exposure to dehumidified cabin air. Generally speaking, one should take about a cup (240 mL) of water every hour when flying. So a typical 4 to 6 hour flight would require 1 to 1.5 L of active rehydration - which very few individuals are able to maintain. Social concerns about disrupting other passengers due to more frequent trips to the bathroom may also encourage subtle, self-imposed fluid-restrictions. Conversely, on-board access to pro-diuretic drinks (i.e., alcohol or caffeine-containing beverages) promotes fluid losses. Consequently, nearly all divers will arrive at their destination in a state of at least minor dehydration.

How do we know we are dehydrated & what can we do?

In general, the colour of urine is a good indicator of an individual’s state of hydration: the lighter it is, the less concentrated it is. This means the body is well-hydrated and has no need to employ water-conserving strategies. However, diuretics such as alcohol, coffee and medication interfere with the body’s water conservation systems; diluted urine may then be produced even in a state of mild dehydration which makes the urine colour less reliable. Dark or small quantities of urine are signs of dehydration. As the state of dehydration progresses, symptoms start to develop which range from minor to life-threatening:

Mild to Moderate dehydration:

  • Thirst (note: this means that if you are thirsty, you are already dehydrated. Don’t use thirst as a prompt for rehydration; anticipate the need to maintain or recover fluid losses)
  • Dizziness (not always recognised by the individual)
  • Headache
  • Muscle cramps
  • Tiredness
  • Dry or sticky mouth
  • Dark coloured urine and decreased urine output


  • Extreme fatigue and weakness
  • Extreme thirst and very dry mouth
  • Sunken, tearless eyes
  • No urine passage for 8 hours
  • No perspiration / dry skin with loss of skin tone and flexibility (note: in older individuals the skin tends to stay “bunched up” for a period of time when pinched)
  • Rapid heartbeat, weak pulse
  • Rapid breathing
  • Low blood pressure
  • Irritability and confusion
  • Seizures
  • Depressed state or eventual loss of consciousness 

Most dehydration is mild and can easily be reversed by drinking more water. The use of Oral Rehydration Salts or Isotonic Sport Drinks, in addition to water, may also be considered. These replace salts and electrolytes which is further enhanced by the addition of appropriate quantities of glucose. This is particularly important in the case of diarrhoeal illness or vomiting. Once severe symptoms are apparent, immediate medical care is required.

How to avoid dehydration?

It is much better to avoid dehydration than to treat it. Moreover, only by avoiding it can divers reduce the risk of DCS. In addition to taking fluids, additional water losses can be mitigated by:
  • Rinsing off sea water and salt crystals from the skin
  • Avoiding hypo- or hyperthermia  by wearing appropriate protective clothing and only donning thermal protection suits right before the dive
  • Avoiding or restricting alcohol and caffeine consumption and compensating for any diuretic losses by deliberately increasing water intake
  • Limiting sun exposure and preventing sunburn.
As for the guidelines for water intake: Although possibly counter-intuitive, taking in infrequent, large quantities of water is not ideal; it tends to promote diuresis rather than sustain optimal hydration. Therefore sipping a litre of water over an hour is better than gulping it all down just before plunging into the sea. In general, the daily intake of water should be increased by about 2 litres above the usual maintenance volumes of about 1.5 to 2.5 litres. If the risk for food contamination makes these acceptable (which is not always the case in tropical destinations), fresh fruits and vegetables provide additional sources of water. Some manufacturers even produce drinking sachets for use under water. This is not for novice divers, however, as breath-holding, choking and even water aspiration may occur unless this is done safely. It is therefore best to experiment under controlled conditions before doing this in open water.

The DAN "More Water, Less Bubbles" safety campaign.

DAN started the "More Water, Less Bubbles" campaign at the end of 2012. Articles in Alert Diver magazine and on the DAN website have been supplemented recently with dehydration awareness surveys and specific information on how to avoid dehydration and lower the risk of DCS. DAN has also brought out an aluminium drinking bottle with the campaign's slogan: "More Water, Less Bubbles" which refers to correlation between adequate hydration and a reduced risk for bubble formation and growth.

Additional Information

Research published in March 2008 on -- ‘Preventive effect of pre-dive hydration on bubble formation in divers’ by E Gempp, J E Blatteau, J-M Pontier, C Balestra, P Louge has shown that pre-dive hydration significantly decreases circulatory bubbles, thereby confirming the benefits of rehydration in reducing DCS.
Additional Research by DAN Europe on Surface Tension (ST) has provided support for the mechanisms involved: In simple terms: pure water has a high ST which means that bubbles tend to collapse on themselves. The more concentrated (dehydrated) plasma (or urine) becomes, the lower the ST becomes thereby making it easier for bubbles to form and grow. This is analogous to adding a detergent to water. In the graph below (left) Urine ST is shown to follow Blood and Plasma ST and, of course, the former is much easier to measure in practice. Accordingly, the graph on the right (showing Urine ST) is able to show that active rehydration raises Urine ST (and by implication Blood and Plasma ST) which would be expected to limit or prevent bubble growth, whereas the opposite would be expected as ST drops. The bottom line – drink water regularly while diving: “More Water, Less Bubbles”.

Circulating Bubbles detected by Precordial Doppler after a 45 meter, 20 minute dive in normohydrated and hyper hydrated subjects. Hydration significantly reduces the amount of circulating bubbles