Understanding Scuba Diving and Dehydration – The Effects and Why It Matters

When the Bends Isn’t the Bends

Over the years, I’ve lost count of how many times a scuba student has surfaced in a panic, convinced they had the Bends. Their fingers were cramping. They felt dizzy. Foggy. Weak.

More than once, out of caution, I’ve made the call to activate the dive rescue team. It might begin with just a phone call, and then an escalation of a callout. And every single time, after physicians and nurses completed their evaluations, the diagnosis was the same:

Dehydration.

It’s a powerful reminder of how easily dehydration and heat exhaustion can mimic decompression sickness (DCS). The overlap in symptoms is striking:

Muscle cramps or joint pain
Dizziness or lightheadedness
Confusion or difficulty concentrating
Fatigue or unusual weakness
Headache
Nausea

When you’re new to diving and you feel your hands seize up or your head start to spin after a dive, it’s terrifying. The word “Bends” carries weight, and it should. DCS is serious and potentially life-threatening if not treated promptly.

But so is severe dehydration.

Surrounded by Water, Yet Still Dehydrated

There’s a strange irony in diving. You can spend an entire day immersed in water and still end up significantly dehydrated.

The problem is that immersion masks fluid loss. You don’t feel sweat evaporating. You’ve probably drank some water, and then peed it back out. You don’t notice how much fluid your body is shifting. By the time symptoms show up, you’re already behind.

Divers often assume, “I’ve been in water all day, I must be fine.” Physiologically, that couldn’t be further from the truth.

dive boat kuta lombok — Photo by Blue Marlin Dive Kuta Lombok

What Diving Really Does to Your Body

Diving is more physically demanding than many people realise.

You’re hauling heavy gear in the heat
You’re suiting up in thick neoprene under direct sun
You’re breathing dry compressed air
You may be running on caffeine and nerves

Then there’s immersion diuresis, the increased urge to pee, a normal physiological response where your body increases urine production because it interprets water pressure as fluid overload. In simple terms: your body thinks it has too much fluid and starts getting rid of it.

Add saltwater exposure, wind, exertion, and adrenaline, and you’re losing more fluid than you realise.

Dry Air, Circulation, and Off-Gassing

Every breath from a scuba tank is extremely dry. Over the course of a dive, that dry air pulls moisture from your respiratory tract.

When you’re dehydrated, blood volume decreases and becomes more concentrated. Thicker blood doesn’t circulate as efficiently, and efficient circulation is critical for eliminating dissolved nitrogen after a dive.

Hydration is not a magic shield against decompression sickness. It doesn’t make you immune. But good hydration supports circulation, tissue perfusion, and your body’s natural ability to off-gas efficiently.

When Dehydration Looks Like the Bends

This is where fear escalates.

Muscle cramps
Joint aches
Dizziness
Headache
Fatigue
Mental fog

These symptoms overlap heavily with DCS. I’ve watched students spiral into panic, convinced something catastrophic was happening.

From an instructional standpoint, suspected DCS is always treated seriously. If there is doubt, we activate emergency protocols.

But the pattern I’ve seen again and again reinforces an important truth: basic physiological stress can be masked as something far more ominous.

The symptoms are real. The fear is real. But the cause is often simpler than imagined.

The Heat Factor Divers Underestimate

Boat Diving in Puducherry — Photo by Tushar “TC” Chaudhary

Most dive days include long surface intervals in direct sun. Boat decks radiate heat. Wetsuits trap it. In tropical water, your body works hard to regulate temperature.

Heat exhaustion compounds dehydration quickly. Together they amplify weakness, nausea, dizziness, and confusion.

Many divers underestimate how draining the surface portion of diving truly is. Gearing up, swimming out. Ironically, the time between dives can be more physiologically stressful than the dive itself.

The Habits That Work Against You

Dehydration rarely comes from one dramatic mistake. It’s usually a series of small ones:

Coffee instead of water in the morning
Avoiding fluids because you don’t want to pee in your wetsuit (guilty!!)
Alcohol the night before (double guilty!!!)
Forgetting to drink during surface intervals
Relying on soda instead of water

Coffee, tea and soda do contribute to overall fluid intake, they’re mostly water. But they aren’t ideal primary hydration strategies in heat and physical exertion.

Caffeine has a mild diuretic effect (especially in higher amounts) and can mask fatigue. High-sugar drinks slow gastric emptying and can contribute to energy crashes. They’re not useless, but they’re supplemental, not foundational.

Water remains the baseline. Low-sugar electrolyte solutions can help during prolonged heat exposure. That Powerade, powered sugar electrolytes, even a fresh coconut.

Hydration Is Safety Equipment

We talk extensively about dive computers, redundant air sources, emergency action plans, and conservative dive profiles, and we should.

But hydration belongs in that same safety conversation.

Proper fluid intake before and between dives supports:

Circulation
Mental clarity
Muscle function
Thermoregulation
Overall physical resilience

It may reduce the severity of symptoms that mimic DCS. It may support more efficient nitrogen elimination. It certainly reduces avoidable anxiety and unnecessary emergency activations.

Sometimes the difference between a calm, confident diver and a panicked one isn’t technical skill.

It’s preparation.

The Real Takeaway

This isn’t about downplaying decompression sickness. If DCS is suspected, it is always treated seriously.

But it is about recognising how easily dehydration and heat stress can imitate it.

Divers love advanced gear and new technology. Yet one of the most powerful safety tools requires no batteries, no firmware updates, and no certification card.

It’s a water bottle, used consistently.

Dive smart.
Hydrate early.
Hydrate often.