It's been a year since Johanna Pakenham went into a coma after drinking almost five litres of water.

The marathon runner from Andover, Hampshire ran over the finish line of the London Marathon last year, to then be rushed to hospital hours later.

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 Journalist: Emily Ford