Thanks for all of the responses, I thought as much. I live in Indiana with moderate weather, though last summer it was always in the 90s to even 100 degrees and above. My pool outside is not heated nor underground but it kept me cool. I suppose after being out in the hot weather for days and days it would heat up to where it wouldn't help. My boyfriend made a comment that seeing as the heat directly effects sunburns in game it may have something to do with the water only helping to increase sunburns (as it does so in real life).
Just my thoughts on it, part of me wishes there were a few more ways to cool off now. Just going inside or opening a parasol seems very limited. I'll definitely look into sprinklers though (I usually don't get them unless I have a garden because I get sick of Sims autonomously going out there in between times when I queue up things). Maybe I'll do some tests on other things that can cool your Sim off... like those Slip-n-Slides they have.