While playing the sims 3 I found out that you can very easily can the depths of pools. So you can pretty much make a pool that can be really shallow like a spa set up or really deep.

First Step
Build a pool that you want to make shallow. It can be any size you want.

Second Step
Ok I want to make my pool very shallow, so I am gonna to make the depth 4 clicks deep. To do this find land near your original pool and raise the land up 8 clicks (12-8=4). Then build another pool on the 8 click land.

Third Step
Next turn open the cheat window by holdin shift + ctrl + c and type in the cheat constrainfloorelevation false.

Fourth Step
Then from the floor of the new pool on the 8 click land take the leveling land tool and level from the floor of the new pool to the floor of the original pool.

Fifth Step
Then you will get this shallow pool!!!

Additional Stuff
You can make the pool depth deeper. I made a pool deeper by lower the land 4 clicks and leveling that pool floor to the original pool floor. However, I couldn't upload the picture because the file was too big

IMPORTANT!!!
Side Effects of changing pool depth. When you change the pool depth to make the pool shallow, the sim does not swim in the pool at the right level, instead the sim will swim, lets stay as in my example, 8 clicks above the pool. So I guess someone can attempt to make a fake floating pool, I know I tried it. When you make the pool depth deeper, your sim will swim deeper. ALSO if you make the pools too deep your sims will drown and die.