May 2019

Why does Scuba Diving make you want to Pee?

By Mike Waddington

Anyone who has spent a bit of time on a dive boat will know that they often smell like a dark corner near your local pub – or in other words, they smell like urine.

Most divers are too ashamed to say it, but the vast majority of us feel the overwhelming urge to pee while we are underwater, and it doesn’t matter if you went only just went to the toilet before jumping in. Just a few minutes after deflating your BCD and dropping down, that urge comes back again.

But why does diving make us need to urinate more often than normal?

Well, there are actually a few scientific reasons behind it, so next time someone comments on your smelly wetsuit, tell them it’s science, and not your fault.

After all, there are only two types of divers in the world – those who pee in their wetsuits, and those who lie about it.

Remember your Open Water Course?

Lets start with the easy answer.

If you think back to your Open Water course, you may remember your instructor telling you how important it is to be properly hydrated while diving. Dry air, exertion, and exposure to salt water will cause you to lose fluids, and it is vital that you replace it. You were told to drink lots of water before and after your dive, and in between dives if you were doing multiple dives on the same day, so if you are following your instructors advice, you will naturally need to urinate more.

Dive boats usually have an almost infinite supply of tea and coffee – both of which are a great way to warm up after spending an hour submerged in the water. Unfortunately, both of them are also mild diuretics, which means drinking them will make you need to urinate soon after.

Can Constricting Equipment be the Culprit?

When we dive, we area loaded up with things we would never wear above the water.

Equipment such as weight belts and wetsuits tend to be tight fitting, and that additional pressure on body will stop our body from being as expandable as it normally is. Tight fitting jeans and trousers that put extra pressure on the groin area often increases the need to urinate. Surely a tight fitting wetsuit will have the same effect.

Immersion Diuresis

Even though we tend to drink more fluid when we go diving, there is more at play than just being well hydrated. Physiology has a lot to do with it too.

A phenomenon known as ‘immersion diuresis’ takes place when we are submerged in water.

Even the warm waters found in popular diving destinations such as the Red Sea, Thailand, or the Caribbean is cooler than our body temperature is supposed to be. Our bodies cool much quicker in water than in air, and when our bodies cool too much, the body responds by narrowing the blood vessels to the extremities and redirecting the blood to the central organs – the lungs, heart, etc.

This vasoconstriction primarily draws blood away from the skin, but also the muscles in your arms and legs. You might have noticed you sometimes have blue lips or fingers after diving, even when you don’t feel cold. Well, this is the reason why.

Our kidneys, which control our urine production, sees this overload of fluid to the core organs as a problem, and in turn, stops producing an antidiuretic hormone and begins producing urine to reduce the circulating blood volume, which is the bodies natural response to conserve blood volume.

The exact same thing happens in the winter, where many people complain about having the urge to go more than normal.

Does Gravity Have Anything to do with it?

Let me start of by saying that I am not a doctor, nor a scientist.

There is a common belief (shared by many in the dive industry) that the reduction of gravity while diving causes us to urinate more. This has been shown with astronauts, as the lack of gravity causes the blood to leave the lower body and pool in the central and upper body areas, which in turn causes the bladder to fill quicker.

However, after scouring the internet for answers, I’m going to go against the popular belief and say this is false, although if you can prove otherwise, I would love to hear from you.

Why do I think this is false? Simply because we are still under the exact effects of gravity while we are underwater.

If you don’t believe me, here’s an experiment you can try now and the next time you dive. If you do a head stand right now, you will get a head rush as gravity pulls more blood to your head than is normally there. If you go upside down on your next dive, the same thing will happen, and it will happen in exactly the same time frame. The same thing does not happen to astronauts, as when there is no gravity, there is no such thing as up and down.

Or another simple test? Drop a rock underwater. I guarantee you it will sink. Drop a rock in space, and it wont do anything.

While scuba diving, gravity is still exerting its invisible power on both you and the world around you. The feeling of weightlessness you feel is from the density of water helping to suspend you in the water column, and your BCD and body airspace’s containing air, which naturally wants to float to the surface. If you deflate your BCD or overweight yourself, I am certain you will sink like the rock we hypothetically dropped earlier.

We get that uncomfortable urge to urinate when the bladder is roughly two thirds full, and the weight of the urine is pushing on the bottom of the bladder. Zero gravity has a far more unusual and unpleasant effect on the bladder than making you need to pee more often. As the bladder fills in a zero gravity environment, the urine is suspended rather than sinking to the bottom. This means the bladder can completely fill without the astronaut even knowing about it – that is until they start peeing themselves.

This pretty much proves gravity has nothing to do with it, as if it did, you wouldn’t have the urge to pee – you would just do it.

pee in your wetsuit

Should I Pee in my Wetsuit?

This is entirely up to you really.

It can dangerous to hold your urine over a prolonged period, however holding it in for an hour isn’t likely to cause any urinary tract infections or kidney stones. That being said, having spent a week in an Indonesian hospital after experiencing both simultaneously, I would rather not risk it.

If you do go in your suit, you should do every one a favour and rinse your wetsuit before pulling it on the boat, and make sure you wash it properly afterwards, as an unwashed wetsuit can cause skin conditions and rashes, however contrary to popular belief, it wont damage your wetsuit.

‘Why does scuba diving make you want to pee?’ was written by Mike

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Mike Waddington

I first discovered diving in 2008 after going snorkeling on the Great Barrier Reef in Australia. After trying diving at a flooded quarry in England I decided to head out to warmer more interesting waters in Thailand where I ended on the Island of Koh Tao completing my Open Water course. Instantly addicted with money to spend and plenty of time on my hands I decided to continue until I became a Divemaster so I could live what seemed as the perfect life.

After that I headed to the Caribbean to an island called Utila to complete my instructor course, I spent several months out there completing the MSDT internship, teaching students and leading dives. This is also where I discovered my interest in the technical side of diving, taking part in equipment repair courses and learning about blending gasses and running compressors.

With all my new qualifications it was time to head back to where it had all started, Back to Koh Tao where I intended on living the dream. Once I arrived I quickly found a job and started teaching straight away. During my time on Koh Tao I took part in all many technical diving courses, learning how to dive with re-breathers, in caves and even going down to 90m/300ft!


PADI Master Scuba Diver Trainer
PADI/DSAT Tech Deep Instructor
PADI/DSAT Gas Trimix Gas Blender
PADI/DSAT Trimix Diver
TDI Intro to Cave Diver
TDI Advanced Wreck Diver
TDI Inspiration rebreather Decompression Procedures
PADI Professional Videographer
BSAC Compressor Operator
TDI Equipment Service Technician

Dream Dive Locations:

Silfra, Iceland
Cenotes, Mexico
Chuuk Lagoon, Micronesia
Ice Diving in Russia