Water pumps fail for three main reasons (although there are other mitigating circumstances): use of the wrong coolant, failing to purge and replenish coolant that has been in the system too long, or simply wear and tear over years of use.
Whatever the reason, the best results can be achieved by renewing as many parts of the assembly as you can afford. New always beats old!
Other parts that you may wish to consider:
As with all mechanical assemblies, the more parts you can afford to renew the better the resulting assembly will be.
Add as many items as you wish to the same shopping cart, new seals, fasteners and hoses for example, and still only pay the same fixed price shipping cost.