Dehydration in the Elderly

I lost this link, so you'll have to trust me on this one:

As people age, the part of their brain that tells whether there is enough water intake begins to malfunction. The brain underestimates the amount of water intake required to prevent dehydration. Thus, the person is always close to dehydration.

The only practical answer is to double the intake of water during the day from the amount that seems right.