Take the sides off next to the motor, it has thump screws. Then take the back off, between the ski locker and the engine compartment, it also has thumb screws. You may have to use a little foot power to unwedge that back part. All you have to do is push out the back panel maybe a foot to get access to the water pump and impeller.
Look up toyotafreaks post on this subject. He has an S22 as do I and I used his directions. Very easy to follow once you get access.
Dennis