Dehydration
Dehydration and Diving
You’ll often hear Dive Rutland staff reminding you to drink water before and after diving. There’s a good reason for this—hydration has a direct impact on both performance and diver safety.
Dehydration isn’t just discomfort. In diving, it is a recognised contributing risk factor for decompression sickness (DCS).
What is Dehydration?
Dehydration occurs when the body loses more fluid than it takes in. Even mild dehydration affects circulation, thermoregulation, and physical performance.
The human body is made up of roughly 40–75% water, and it constantly regulates fluid balance through urine production, sweating, and respiration.
A high-protein diet can increase fluid loss because more water is required to process nitrogen waste.
How to Spot Dehydration
A simple indicator is urine colour.
Dark yellow or amber urine usually indicates dehydration. Pale straw or light yellow suggests good hydration. Output volume also matters—low volume often indicates dehydration.
These are general guidelines, but they are widely used and effective in most healthy individuals.
Why Dehydration Matters to Divers
Dehydration reduces blood plasma volume. This thickens the blood and reduces circulation efficiency.
That matters in diving because blood is responsible for transporting oxygen and removing inert gases like nitrogen.
Reduced circulation can slow off-gassing and increase the risk of DCS.
Gas Exchange and Off-Gassing (In Simple Terms)
Gas exchange happens in the lungs, where oxygen enters the blood and carbon dioxide is removed.
In diving, nitrogen is also absorbed under pressure and must be eliminated safely during ascent.
Off-gassing is the process of releasing that dissolved nitrogen as pressure decreases. If ascent is too fast—or circulation is compromised—nitrogen can form bubbles in tissues and blood.
Effects of Dehydration on the Body
Dehydration can lead to:
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Reduced physical performance (up to 8–10%)
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Lower cardiac output and stroke volume
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Reduced oxygen delivery to tissues
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Headaches and reduced concentration
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Muscle cramps and fatigue
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Electrolyte imbalance
All of these can negatively affect dive safety and decision-making.
Common Causes in Diving
Breathing Dry Compressed Air
Cylinder air is extremely dry. The body must humidify every breath, increasing fluid loss through respiration.
Immersion Diuresis
Cold water and pressure cause blood to shift centrally. The kidneys respond by increasing urine production, increasing fluid loss.
Heat, Sun and Exposure
Warm conditions, wetsuits, and drysuits increase sweating—even in the UK. Wind and sun accelerate fluid loss.
Saltwater Exposure
Salt left on the skin draws moisture out, contributing further to dehydration.
Travel and Flying
Aircraft cabin air is very dry. Without adequate water intake, divers often arrive already dehydrated. Aim for regular water intake throughout flights.
Illness and Medication
Vomiting, diarrhoea, and certain medications can significantly increase fluid loss.
Alcohol
Alcohol increases urine production and directly contributes to dehydration. It is also incompatible with safe diving practice.
Signs and Symptoms
Mild to Moderate Dehydration
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Thirst (a late indicator)
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Dry or sticky mouth
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Headache
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Dizziness
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Muscle cramps
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Light-headedness on standing
Severe Dehydration (Medical Attention Required)
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Extreme thirst and very dry mouth
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Rapid pulse and breathing
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Weakness or confusion
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Poor skin elasticity
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Significant drop in blood pressure
Prevention
Hydration should start before you even get in the water.
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Drink water regularly throughout the day
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Avoid alcohol before diving
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Keep exposure suits off until needed
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Rinse off saltwater after dives
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Use shade and sun protection
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Maintain hydration during travel and flights
A practical target is consistent small amounts of water throughout the day rather than large amounts infrequently.
Key Message for Divers
You are always losing fluid when you dive—through breathing, pressure effects, temperature regulation, and environmental exposure.
Dehydration increases fatigue and can elevate DCS risk.
Drink water regularly before, between, and after dives. Every site visit is a refill opportunity—use it.