Since the Water Pump (WP) is driven by the Timing Belt (TB) It is HIGHLY recommended to replace all the moving parts while the WP is being replaced.
Being a 2003 , your TB must be close the MANDITORY replacement milage. Replace all moving parts while the engine is torn apart. (Pullies, tensioner, TB, WP, crank Seal, Cam Seal...etc)
If you try to save a few $$ by doing the job cheap.... the parts you DO NOT replace will fail before the next MANDITORY TB change. When these parts fail, they will likely damage the TB.
A damaged TB will cause pistons to hit valves causing MAJOR engine damage.
Also, although not manditory.... I recommend installing WP with BRASS impeller. The factory WP has plastic impeller which has been known to have issues. (Plastic impeller breaks off of the shaft and stops pumping antifreeze... engine overheats)
Source: Personal experience