Why you need to wee more when you scuba dive

A question that was raised by one of our divers on a recent trip… Why when on dry land can I go for hours and hours not needing a wee, but as soon as I jump in and start a lovely dive then I need to go.

So I thought it was a great question and lets do some research, and there is a scientific reason why you need to wee more when you dive… it’s not just the fact you are in the most awkward clothes to get out of to have a wee !!


So why do we need to wee more – I’m changing from my wetsuit to a white coat for a little science, first – what makes you need to wee..

The human body is full of blood. The volume of blood may increase or decrease with eating, drinking and other factors. The body regulates the amount of blood in the body in a very clever way – When the volume of blood in the body increases, the extra blood flows through the veins to the heart. The heart senses the increased volume of blood and nerve sensors in the heart tell the kidneys to release urine. This removes fluid in circulation and reduces blood volume.

So – what does Scuba diving have to do with it..

Cold Water & Gravity

  1. Cold Water immersion diaereses – This is the bodies automatic way to minimize heat loss, when you get into the water the body reacts (called the mammalian reflex) and sends blood to the vital organs so therefore increases the amount of blood in the heart and this starts sending signals to the kidneys to make you wee.. that pesky heart!

    Did you know as soon as you put your face in cold water it can drop your heart rate by 10 – 20% (and free divers train to drop it to even 50%) – I always wondered why my mother-in-Law splashed the kids face with cold water to calm them down when having a tantrum.. there is actual science behind it!

  2. Gravity – or lack of it – Weightlessness or near weightlessness,
    also causes blood to shift Paradise Divers - 11Jun2014 (16)towards the body’s core, This fluid shift was first observed in astronauts, who had to wee more than normal while in space. If you have perfect neutral buoyancy, it is like you have defeated gravity, and thereforeHover the blood collects around the heart, and like cold water immersion diaeresis tells your kidneys to make you wee.



So needing to wee when you are diving is NORMAL – it’s your bodies way to protect itself – you and I both know we don’t need our body to protect us from Scuba diving, but it doesn’t think being under the water for an hour is normal so makes us get out to wee

There is no way around it, I always encourage divers to go before they dive to try and reduce the impact. It is still really important to drink water, (avoid drinks with caffeine as this is a diuretic so will also make you need to wee) being dehydrated can increase the risk of DCS, give you headaches and increases cramps.

So there is no magic formula to make you need to wee less while diving, if you have your own wetsuit or semidry (a semidry tucked into your boots is very good at retaining the liquid inside it..) and you need to go then it’s your choice if you wee in it… make sure you rinse it thoroughly and yourself as well, it is 95% water.. but it’s still wee.

If it’s a rental suit it is frowned upon to wee in it – although all ours are dunked in a disinfectant after every dive, its still not pleasant for the next person.

If it’s a drysuit (and you don’t have a pee value) just don’t do it – you won’t have any buddies left who will unzip your suit, or share the car journey home!

From now on you know that it is normal that you need to wee when you dive – every diver feels it, it’s not just you getting old and incontinent, it’s your pesky body sending blood to the heart that makes you wee.

Happy Diving


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