We’re told that most of us don’t get enough water and many of us are borderline dehydrated. However, doctors warn that drinking water in excess can actually be poisonous, leaving us with fatally low levels of salt in our blood.

Doctors publicize this warning after an unnamed woman in the United Kingdom almost died as a result of drinking too much water while treating a urinary tract infection (UTI). The woman’s doctor told her to drink plenty of fluids, though it is unclear if she interpreted this to mean half a pint every 30 minutes or if the doctors actually told her specifically to do this.

The woman was rushed to the emergency department of her local hospital where she was in dire straits, as her blood showed dangerously low levels of salt. This condition is deadly in about 30% of people afflicted with it.

Attending doctors described their patient in a written document:

“During her visit to the emergency department, she became progressively shaky and muddled. She vomited several times, was tremulous and exhibited significant speech difficulties.”

The woman was hospitalized for 24 hours and has reported that she is unable to remember long periods of time during her stay. She told news outlets it took her a week to feel normal again, though she says she still feels unusually tired.

Those who take recreational drugs and are particularly active may also be at risk for low levels of salt in their blood, which is why doctors warn against drinking water in excess.

But how much water is too much? Well, there’s the rub. Doctors don’t actually know, which causes frustration on both the part of the patients and the medical community. There is little guidance in any medical journal to substantiate when too much water becomes dangerous.

Dr. Imran Rafi, chairman of clinical innovation and research at the Royal College of GPs attempts some advice for those who are curious:

“We would encourage patients to drink more if they have symptoms of dehydration, such as feeling thirsty – including in hot weather or when exercising – or passing dark-coloured urine. There is no steadfast recommendation as to how much water people should drink in order to stay healthy, but the key thing is to keep hydrated – and passing clear urine is a good indication of this.”

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