Of all the ways you can think of dying in space – shapeshifting aliens, robot loses its mind and tries to kill you, potato chips fly into the console, etc – drowning is probably furthest from every astronaut's mind.

Yet in July 2013, astronaut Luca Parmitano faced just that scenario while conducting a spacewalk outside of the International Space Station (ISS). In one of the most dangerous incidents in spacewalk history, Parmitano was conducting an Extravehicular Activity (EVA) planned to last six hours when he noticed water building up inside his helmet. He informed NASA of the situation, but for a time they did not realize how serious the incident was.

For a full 23 minutes, he remained outside of the ISS while the liquid continued to grow, and move around inside his helmet. By the time he was pulled indoors, it had made its way into his eyes, and close to his nose and mouth, commonly known in astronomical terms as "those holes in your face you need to live".

"As I move back along my route towards the airlock, I become more and more certain that the water is increasing," Parmitano wrote of the experience in his European Space Agency blog. 

"I feel it covering the sponge on my earphones and I wonder whether I’ll lose audio contact. The water has also almost completely covered the front of my visor, sticking to it and obscuring my vision."

He realized that to get back into the station, he was going to have to adjust his body position, flipping around entirely.

"At that moment, as I turn ‘upside-down’, two things happen: the Sun sets, and my ability to see – already compromised by the water – completely vanishes, making my eyes useless; but worse than that, the water covers my nose – a really awful sensation that I make worse by my vain attempts to move the water by shaking my head.

By now, the upper part of the helmet is full of water and I can’t even be sure that the next time I breathe I will fill my lungs with air and not liquid."

Unable to see, he became disorientated and couldn't tell which direction would take him back to the safety of the airlock. His vision is compromised to the point that he can't even see the handles on the outside of the space station that are used to move around on EVAs. Then his radio became so quiet, he could not hear his colleagues. He was alone, blind, and unable to hear. In space.

Keeping remarkably calm, given the circumstances, he began to feel his way along his cable towards the airlock, locating the handles by fumbling, all the while wondering what to do if the water were to reach his mouth.

"The only idea I can think of is to open the safety valve by my left ear: if I create controlled depressurisation, I should manage to let out some of the water, at least until it freezes through sublimation, which would stop the flow. But making a ‘hole’ in my spacesuit really would be a last resort."

He finally managed to fumble his way back into the airlock, where he waited with his eyes closed. He hadn't heard an instruction from NASA since he was told to ignore all usual protocols and head back in. Eventually, he felt the vibrations of Chris Cassidy entering the airlock and shutting the door, but his ordeal was not yet over.

His radio was now functional but only one way. He could hear instructions, but they couldn't hear him. And then, as water entered his ears, he couldn't hear once more. 

"I’m completely cut off. I try to move as little as possible to avoid moving the water inside my helmet. I keep giving information on my health, saying that I’m ok and that repressurization can continue. Now that we are repressurizing, I know that if the water does overwhelm me I can always open the helmet. I’ll probably lose consciousness, but in any case that would be better than drowning inside the helmet."

He felt Cassidy squeezing his glove in reassurance. Eventually, it's safe to take his helmet off and he is pulled out by the team, who are waiting to greet him. He was safe.

Investigations into the incident revealed that contamination had clogged up the filters in his suit, leading to the buildup of fluid. The same had happened on a prior spacewalk, but had been put down to a leaking water pouch.

"Space is a harsh, inhospitable frontier and we are explorers, not colonisers," he concluded in his blog. "The skills of our engineers and the technology surrounding us make things appear simple when they are not, and perhaps we forget this sometimes."

"Better not to forget."