The accident occurred after his apartment building turned off the water so that a contractor could install a backflow prevention valve.
The 58-year-old man — who now plans to sue the building's management company — pulled the toilet handle around 11 p.m. to test the water pressure, and the bowl exploded in what he called a "porcelain bomb."
He was briefly knocked unconscious and required 30 stitches that left a scar across his face.
According to a lawyer for the co-op, four other toilets in the building also exploded.
"The only conclusion anybody has reached — and they're still investigating — is that there was a buildup of air pressure in the pipes so that when it came back on, the pressure was just pushed through the pipe and caused the explosion," she told AFP.