Todd ran across a great set of videos for arm exercises.
In looking at some of my baseball websites I can across this site that already has the videos for the arm exercises. These are the ones I have used. Of course for water polo they should do them for both arms.
http://www.asmi.org/SportsMed/throwing/thrower10.html
They don’t talk about # of reps or sets but I’d start with 1 set 10-15 reps and then go up from there.