I thought I had seen something about "water poisoning" before:
LEAH BETTS DIED OF DRINKING WATER TO COUNTER DRUG'S EFFECT
By Jeremy Laurance, Health Correspondent
Leah Betts, the teenager who collapsed after taking an Ecstasy tablet, died as a result of drinking too much water, which made her brain swell.
Doctors who treated her at Broomfield Hospital, Chelmsford, Essex, where she was taken after lapsing into a coma at home during her 18th birthday party, will tell the coroner that "water intoxication", and not an allergic reaction to the drug, was the cause of death. The inquest into her death is to open in Chelmsford today but is expected to be adjourned. The coroner will receive a post-mortem report by the Home Office pathologist Dr Paula Lammis.
Water intoxication occurs when a person drinks so much water - a minimum of three litres - that the blood becomes diluted. Laboratory results show that on admission to hospital hours after taking the 10 pounds tablet, Leah's plasma sodium level - a measure of how dilute her blood had become - had fallen to 126 millimoles per litre compared with a normal range of 134 to 145.
As a result, water was sucked into her brain cells under osmotic pressure, causing them to swell. This increased pressure on the brain stem, resulting in coma and death.
Overheating and dehydration are known risks of taking Ecstasy, a stimulant which can keep young people dancing for hours, and drug agencies advise users to drink plenty of water and take frequent rests.
more at:
http://www.urban75.com/Drugs/drugxtc1.html