Not all older dogs drink more water however some older dogs do drink more water and it's usually caused by a condition known as polydipsia.
The condition polydipsia causes the dog to lose water in it's body in excess so the dog needs to drink more water to make up for the loss of water in their body.
Other problems that can cause a dog to to drink more water the older they get is kidney failure, diabetes mellitus and Cushing's disease.
So if your dog is drinking more water than normal it would be a good idea to have the dog checked out for any of those diseases if possible.
But usually it cannot be fixed especially if the diseases have progressed and dogs normally have a lifespan of 12 to 18 years.
So the dog may not live much longer anyway.