Daniel Chong, 24, is still weak after his ordeal. He spent several days in intensive care, being treated for near kidney failure.
The University of California, San Diego student was swept up as one of nine suspects in an April 21 drug raid. He was told he would be released and not charged.
Instead, he was handcuffed in a tiny cell to await release. Drug Enforcement Administration spokeswoman Amy Roderick said he was accidentally left there.
"As soon as they said they were going to let me go, that door never opened, and I never got released. I did what I had to do to survive. I cycled through my own urine," said Chong.
Chong said he screamed and banged on the door, but nobody came even though he could hear footsteps of people going by. He was finally found on April 25.
"When they opened the door, one of them said, 'Here's the water you've been asking for,'" Chong said. "But I was pretty out of it at the time."
The DEA hasn't commented on Chong's claim that he was without basic necessities for days.
Chong's attorney said he plans to file a claim against the federal government, and if it is denied he will proceed with filing a federal lawsuit.
The Associated Press contributed to this report.