rat tripled water intake

Question
My daughter's rat seems to be taking in two to three of the drinking bottles of water compared to about 1-2 previously.  The rat seems somewhat lethargic.  It is a male, about 2 years old.  This has been going on for 2-3 weeks.  He is eating all of his food.  My daughter says his poo was "squishier" than usual when she changed his rags (we use rags instead of store bedding).  I'm trying to think of anything you might ask!  Is this normal for a 2-yr-old rat?  He's a regular sized rat (he was going to be used for snake food, if that helps with knowing his size).

Answer
Hmmm....has he been urinating more or less?

Unfortunately, Kidney disease is very common in older rats, especially if the diet they have been on has been high in protein.

Let me know if you notice his urine habits and if he has urinary frequency or if it seems like he has not been going as much as he should for the amount of water he is drinking, etc...

What has his diet been during his life time if you dont mind my asking.

Also, do you have a vet that is well versed in rat care?