[Can water be poisonous?].

History And Admission Findings: Two female patients aged over 80 years developed central nervous symptoms after drinking large amounts of water (more than 3 l per day).

Investigations: Both had a hypoosmolar hyponatremia that was induced by concomitant treatment with hydrochlorothiazid (HCT) in the one case and in the other case relied on a distal tubular damage due to reflux nephropathy.

Diagnosis, Treatment And Course: Hyponatremia was corrected after withdrawal of HCT and fluid restriction and central nervous symptoms disappeared rapidly.

Conclusions: Distal tubular urinary dilution can be disturbed by HCT and parenchymal renal disease and can result in symptomatic hyponatremia after drinking large amounts of water.