The risks of dehydration in scuba diving

For professional divers, preparation is second nature. Equipment checks, gas planning, environmental assessments, and emergency procedures are part of every dive. Yet one critical factor often receives far less attention than it deserves: hydration.

Dehydration is subtle, cumulative, and physiologically very impactful. This makes it one of the most underestimated contributors to reduced performance and increased risk in professional diving. Understanding why hydration matters, and how to manage it with intention, is essential not only for peak performance but also for long-term health and operational safety.

Why diving dehydrates you more than you may think

Immersion Diuresis - When the body is submerged, blood shifts to the core due to the increased hydrostatic pressure. This triggers increased urine production as the body attempts to reduce blood volume, a process known as immersion diuresis. The result: potentially significant fluid loss during every dive.

Breathing Dry Gas - Compressed air or mixed gases delivered via scuba systems are extremely dry. With every breath, the body must pull moisture away from the respiratory tract in order to humidfy the air and make it breathable, which accelerates dehydration. This is especially so, on long or deep dives where gas consumption is higher.

Sweating - Wetsuits and dry-suits trap heat. Even in cold water, divers frequently sweat inside their suits during surface prep, descent, and exertion underwater. Since sweat evaporates into the suit, you don’t feel the moisture loss, but it’s happening.

Multi-Dive Days - Professional divers often have to perform multiple dives per day for multiple days. Even mild dehydration becomes compounded, lowering performance and increasing susceptibility to fatigue and decompression stress.

How dehydration affects professional divers

Reduced Cognitive Performance - Decision-making, focus, and reaction time; all essential for complex dives, decline rapidly with even mild dehydration (as little as ~1–2% body water loss).

Increased Risk of Decompression Sickness - Dehydration plays a vital role in decompression sickness (DCS), it also reduces blood plasma volume, which can affect perfusion and inert gas elimination. Poor hydration is widely considered an aggravating risk factor.

Decreased Physical Endurance - Professional divers can involve long swims, equipment handling, dealing with strong currents, or overhead environments. Dehydration decreases muscular endurance and increases fatigue, raising both workload and air consumption.

Thermoregulation Challenges - Hydration plays a central role in heat balance. Dehydrated divers struggle more with both hypothermia and overheating—conditions that can escalate under tightly controlled dive operations.

Hydration strategies

Start Early - Aim to begin hydrating way before the dive, not just on the morning of the dive. Sip consistently rather than bulk drinking right before entering the water.

Use Electrolytes - Water alone isn’t always enough. Electrolyte solutions help maintain the essential minerals that can be lost form perspiration and other fluid loss, and is important when working in the heat or during high workload or multi-dive operations. Choose low-sugar options to avoid energy crashes.

Monitor Caffeine Intake - Caffeine is a mild diuretic and can contribute to dehydration when consumed in excess. It’s fine in moderation, just don’t rely on it as a primary source of alertness before a demanding dive.

Rehydrate Between Dives - Aim for at least 300–500 ml (about 2 cups) between dives, adjusting based on suit type, exertion, and environmental conditions.

Avoid Alcohol - Alcohol is dehydrating and can impair cognitive and physical performance, not ideal before diving or when recovering from a challenging dive day.

Hydration shouldn't be an afterthought

For professional divers, hydration is a critical operational factor, not a casual suggestion. Just as you meticulously maintain equipment and follow decompression procedures, maintaining optimal hydration should be part of your standard pre-dive, intra-dive, and post-dive protocol.

By treating hydration as essential to your diving readiness, you not only enhance performance and comfort but also contribute meaningfully to long-term health and operational safety.