Thanks for all the suggestions here, very difficult to encourage my Mum (age 83 with MM) to drink enough as she lives alone, I just remind her whenever I speak to her. Elderly people are not good at drinking enough anyway and I certainly notice it even in her voice on the phone if she is getting dehydrated.
David – I understand that tea and coffee all count – lots of people think they don't but they are still mostly water so better than nothing. However, alcohol is not so good unfortunately as it definitely causes dehydration – sorry all!
Jill