Matthew Ellis drank "pints and pints" of water, then collapsed and was taken to the intensive-care unit at Northern General Hospital in Sheffield, the Sheffield Telegraph reported.
Family members said they believe Ecstasy had been put in his drink without his knowing while he was out with them on Boxing Day last year.
That, in turn, caused him to crave water and drinking so much of it dramatically decreased salt levels in his body, resulting in a rare brain condition, extrapontine myelinolysis, the Telegraph said.
He never returned home from the hospital, where he died of a chest infection.
His mother, Maureen Ellis, 62, of Gleadless, warned against drinking too much water.
"There's no health warning. Water's good for you if you have a certain amount," she said. "But we want to make people aware not to drink that much.
"Matthew went through absolute hell. It's such a waste of a young life."
After staying out late drinking with friends, his mother said, Matthew went to sleep at the home of his father in Lowedges.
He suffered five seizures in the ambulance en route to the hospital.
His mother said a consultant at the hospital said Matthew must have been slipped an Ecstasy tablet without knowing it.