The last time I spent a lot of time with a partly disabled senior citizen, although she recovered from her stroke pretty well for her age, I worried that she was compromising her recovery by not drinking enough water. She didn't want to go the bedpans or diapers route, and didn't particularly like asking the person staying with her to help her shuffle from armchair to wheelchair to toilet. Staying dehydrated reduced the need for that...but I thought it was taking a toll on my friend's mood and energy level.
Here's a positive report (although it's no longer news) on how a whole batch of seniors reacted to an experiment measuring the benefits of staying fully hydrated, in England:
(For the record, I'm indebted to Ozarque, who is a senior citizen, for this link.)