Yup, basically cells go hypertonic...or is it hypotonic I cant remember...making the cell explode.

Lysis (Greek λύσις, lusis from luein = to separate) refers to the death of a cell by bursting, often by viral or osmotic mechanisms that compromise the integrity of the cellular membrane.

This used to be a problem back in the day when ecstacy was big. Kids would roll then drink way too much water in one night.