My wife had the same. Was also told to make sure she drank at least 2 litres of fluid a day and make sure she had salt in her food.
'Fluid' does not have to be water , fruit juice , milk, tea ,even coffee all count but not alcohol . Alcohol is the only one that actually takes out more fluid than it puts in . She was also told to look at the colour of her pee! it should be a pale straw colour, if it is yellow that is a sign of dehydration and not drinking enough fluid
The current fad for not having salt on anything is causing problems according to her doctor , he is seeing constant problems with salt deficiency. Too little salt causes far more problems than too much , salt is essential to us we can not survive without it.