The water pump should be replaced as part of every 60K/100K service, and/or as part of any front engine service.
A leaking water pump can sometimes cause ignition system problems by leaking onto the crankshaft position sensor below it.

Be sure to thoroughly flush your cooling system, because dirt/debris (such as from a failed pump) can cause premature failure in your new pump or other problems in the cooling system.   (Drain the radiator and remove plugs at front and rear of lower block,  just above oil pan rail and flush until water runs clear)  

Never use 100% water as coolant...even in warm climates use at least 25% antifreeze to properly lubricate the water pump (and/or use a specific water pump lubricant).  

Always use distilled water (not tap water) mixed with your antifreeze.