Marathon runner Johanna Pakenham went into a coma after drinking almost five litres of water.
She had hyponatremia, a condition caused by drinking too much water, diluting all the salts and minerals in the body.
Ms Pakenham now wants people to understand the danger of drinking too much, but nutritionist Johanna Hignett says as a population, we don't drink enough.
Video by Emily Ford
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