If your car is like most, it has an electric water pump. That means that there's no easy way to tell how long it will last. In some cases, they've been known to last the life of the engine, while others have failed within just a few years or even months.
The good news is that they're not too difficult or expensive to replace. Most mechanics will charge between $200 and $400 to do the job, and it should only take them a couple of hours at most.
Of course, this all depends on your particular car and how easy it is to access the water pump. Some models are much more difficult than others, which can add quite a bit of time (and money) to the repair bill.