1. If the water pump drive belt is worn or stretched, it should be replaced. However, most often you have to change the belt because it breaks, so it is recommended to always have a spare belt with you in the car just in case (the same applies to the alternator drive belt).
2. To remove the belt, loosen the nut under the lower auxiliary pulley pivot bolt and then loosen the bolt itself. Screw the adjusting bolt into the pulley bracket so that the belt can be pulled out of the groove on the auxiliary pulley. Remove the belt from the crankshaft and pump pulleys and pass it over the fan blades, turning the latter to make it easier to remove the belt.
3. Install a new belt on the pulleys and check that it can be twisted no more than 90°between the pulleys. Pull on the belt.
4. See alternator drive belt replacement procedure chapter 10.