Before you read the rest  exactly  how much water is he drinking I have 5
cats and there are 6 big dog sized round bowls that we refill every other
day.  You measure a cat intake by mL not in cm amount.  Have you changed
brands for the wet food   some wet food actually have less water in them so
hence the cat would drink more.  This is a link to Phil's site it had the
nutrition part about water check this out and read the rest of my response
below http://www.maxshouse.com/feline_nutrition.htm

Rob  any strange activity for a cat involving eating and or drinking  It has
to meanings ONE PAY VERY CLOSE ATTENTION TO YOUR 4 LEG AND OR  GET YOUR CAT
TO A VET.   Diabetes can come on that quick so can alot of feline problems
unless you get a full workup to find out what is wrong no one out here can
diagnose a problem.

Let me tell you me experience with a feline diseases  my cat rumble is 6 at
3 years of age he was being up on my bed doing his own thing watching me
messing on the computer.  He yelped and went in to a seizure no warning
nothing  that was the scariest moment of my like to see a friend in
distress.  2 of the last 3 years  have been hell.  That is how quick
anything can happen unlike humans who can tell us what is wrong  cat have
sometimes tell tale signs that you need to pay attention to  this is one of
them.

Any odd for an cat activity is a sign that you need to take the cat to the
vet.   There are about 10 things that come to my mind why a cat drinks
excess water and all need vet attention or at least a vet to rule out a
problem.  The least of them is that the cat is not getting enough water from
the food

I hoped this helps  let us know what happens

Matthew

He has been to the vet and subjected to a blood test. That has come
back clear which is a relief.  The vet has said that he is running a
slight temp and may just have had a reaction to his recent jabs.
Hopefully he should be fine in a few weeks.  Thanks for everyones
comments.