(CNN) -- In space, water doesn't just fall down; it pools into blobs. Italian astronaut Luca Parmitano demonstrated this in a recent YouTube video showcasing his hair-washing technique on board the International Space Station -- he squirts water onto his bald scalp, and the water forms a glob that crawls around on top of his head.
"And that's it!" he exclaims, as if this behavior of water seems normal to him.
Parmitano found himself in a far more perilous water-related situation Tuesday -- one that "could have become very dangerous," a NASA spokesman said. NASA is currently investigating what exactly happened.
While on a spacewalk outside the space station with U.S. astronaut Christopher Cassidy, Parmitano reported that his carbon dioxide sensor had failed. And then, he began to feel water on the back of his head.
"I am sweating, but it feels like a lot of water. It's not going anywhere," Parmitano said, in a video of the spacewalk released by NASA. He added later, "How much can I sweat, though?"
Water got into his eyes and around ears. "We couldn't guarantee that he could hear us clearly," said flight director David Korth in a press conference Tuesday. The water also interfered with the communications cap that astronauts wear, said Karina Eversley, lead spacewalk officer, at the press conference.
The flight director told Parmitano to return to the space station's airlock; it wasn't "prudent" for him to attempt to continue his tasks with water around his ears, Korth said.
"As he progressed back toward the airlock, the amount of water that he was reporting started to increase and increase," Korth said. "You can imagine that you're in a fishbowl. So go stick your head in a fishbowl and try to walk around, that's not anything that you take lightly."
Fellow astronauts on the space station banded together to quickly remove Parmitano's helmet, and toweled his head.
Between 1 and 1.5 liters of water had accumulated in the suit itself, not just in the helmet, Korth said.
"He did a great job of just keeping calm and cool and getting his way back to the airlock," Korth said.
In response to a reporter's question about whether Parmitano could have drowned, Eversley said, "He certainly had that risk today, and that's why we took it so seriously and terminated the EVA as soon as we understood that we were dealing with quantities of water and not droplets."
Where the water came from is still unknown, but the explanation is "definitely a leak in the system" because it was an abnormal amount of water, Eversley said.
"We have not seen a problem like this before with this type of quantity of water," she said.
One possible source of water in a spacesuit is the drink bag, which holds 32 ounces of liquid. NASA experts think this is unlikely to have caused the water accumulation in Parmitano's helmet, however. The astronaut said the water "tasted funny," Eversley said.
Another is sweat -- but that would not have created the quantity of liquid reported on the spacewalk, she said.
There is also water in the liquid cooling system that could have potentially leaked, she said. The water that runs through the garment under the spacesuit, to keep an astronaut cool, has iodine in it, which could have accounted for the odd taste.
"You'd certainly be concerned," said former NASA astronaut Dr. Story Musgrave. "It'd be a nasty situation, to fill your helmet up with water."
The quickest solution, based on Musgrave's experience, would be to suck in the water and blow it out downward toward your chest, where it could be absorbed by cloth material in the suit.
NASA has not determined when the remaining tasks that the astronauts would have completed on Tuesday's spacewalk will get done. The activities involve installing backup power equipment to critical station components and preparing cables for a new laboratory module that is due to arrive later this year, NASA said.
The spacewalk outside the International Space Station was planned to last for 6½ hours, but ended after 1 hour and 32 minutes, said NASA spokesman Kelly Humphries.
That makes it, according to NASA's website, the second shortest spacewalk in the history of the space station.
The spacesuit Parmitano wore Tuesday was the same one he wore on his space walk the previous week. Extra suits and suit parts are available on the space station, Eversley said.
Eversley said Parmitano is "doing great" and is "smiling and happy."
Parmitano tweeted on Tuesday, "Thanks for all the positive thoughts!"
Wednesday, according to a more recent tweet, it's "Back to normality on the ISS."
CNN's Deanna Hackney contributed to this report.