Writing on his blog from the International Space Station, Parmitano said he felt liquid on his neck shortly after starting the July 16 spacewalk and was blinded and suffocating as the water slowly rose.
"I feel that the temperature of the liquid is too cold to be sweat and above all I have the distinct sensation it is increasing in volume," Parmitano wrote in a gripping first-person narrative of the incident.
"I don't know if I will have air or liquid in my lungs the next time I breathe.... I realise I no longer know where to go to reach the airlock," he wrote.
Once he was safely back inside the space station and repressuring, Parmitano said he remembered thinking he could open his helmet to let the water out.
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"I will probably lose consciousness but it would be better than drowning in my helmet," he said.
His spacewalk on July 16 was stopped after about an hour and a half, marking the second shortest in the history of the International Space Station.
The 36-year-old made it safely back inside and was unhurt, though NASA experts said he faced the risk of drowning had the ordeal gone on much longer.
US spacewalks have been suspended pending the investigations.
Parmitano concluded his blog post saying: "The skill of our engineers and the technology we have at our disposal make things that are not easy seem easy.