This week's NASA report on a near-fatal spacewalk reads like something out of your worst nightmare.

Italian astronaut Luca Parmitano spent nearly an hour floating in space as his helmet slowly filled with water — up to 1.5 liters — engulfing his eyes, nose and ears. And while his July 16 spacewalk ended safely, NASA now acknowledges the mishap could have killed him.

"[Parmitano] experienced a large amount of water collecting inside his helmet which created several hazardous conditions including risk of asphyxiation, impaired vision, and a compromised ability to communicate," the report states. "The presence of this water created a condition that was life threatening."

As the water collected, Parmitano's concerns were initially dismissed. The report says crew members were under the misperception that astronauts' drink bags leaked frequently, and reacted as if the collecting water was due to that less-serious problem.

In a 16-minute span, however, Parmitano said three times he did not believe the water was coming from the drink bag. Only after he drank the bag's remaining water did the team consider other possibilities. A fellow astronaut surmised urine or sweat may be to blame.

Meanwhile, his helmet was still filling up. Another misperception — that water in zero-gravity would cling to the inside of the helmet and not an astronaut's face — led crew members to underestimate the problem.