It is very common in cars these days for the water pump to be driven by the timing belt (or chain as the case may be). Two of the three cars I presently own (Chrysler 2nd generation LH cars are that way - one with timing belt, one with timing chain).
It bugs me that they did that with the engine that has a timing chain, because otherwise the timing chain could be expected to be undisturbed for the life of the engine. AS it is, just changing the water pump is a semi-major operation running $600 or $700 - and the common logic is that while you're in there expending all that labor to get to that pump, you might as well replace the chain (and of course the tensioner pulley), since the labor for doing that is free. But, likewise, on the engine that has the timing belt, the water pump is routinely replaced at the timing belt change interval of 105k miles (because of the labor).
The pressure on the auto manufacturers is high for very tight integration of the components - driving the WP with the timing belt or chain is tighter integration.
Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')