Does this CMU block wall on pool need rebar?
Do you need rebar? Yes. Concrete and masonry do not withstand tension. Tension is absorbed by reinforcing. Think of a diving board. When you stand on it, it bends. Same with your wall. When there is a stress put on your wall, it bends. On one side it’s in compression, which is taken by the masonry. On the other side it is in tension and needs rebar. 

There are many stresses on your wall, 1) A person (or persons) leaning against the wall, 2) seismic activity, 3) wind loads. 

1) You’ve created a “Guard” as defined by the ICC Code. Guards are required to withstand 200 lbs. applied to the top of the wall. 

Your wall is only 26” high and you’ve designed “an attractive nuisance “. Who doesn’t want to jump off the wall into the pool?  That force on the wall when you jump forward could push the wall over. 

2) Arizona is seismically active. (Northern Arizona is really bad, but Phoenix is active.) Heavy materials are harder to control in earthquakes. 

3) Wind is probably not the governing factor. 

I wouldn’t have any beer parties where a bunch of drunken friends start jumping off the wall or where they could be “horsing around” and stumble into the wall, until it’s checked out. 

Btw, not all walls need rebar. Mass or gravity walls resist stress by shear weight. That’s possible, but highly unlikely and are usually battered (thicker at the bottom than at the top). 

You may need buttresses every 4’ to 6’ on center along the length of wall for added support.