Strange!
This site is a bit worrying...
Cloudy water in the aquarium. What causes cloudy aquarium water? - Algone.com look at the white cloudy water bit. Here's a pic in a fish tank
http://farm1.static.flickr.com/55/14...18733c6804.jpg.
It seems a bit extreme but trying to find out whether this can appear like that in water coolers I found this site
AquaSafe 90 - Home Water Test Strips. It might be worth getting the test because it pretty much covers anything that could be causing the problem.
It still doesn't make sense though, as you would expect there to be more bacteria in the warmer water, and you didn't say anyone was getting sick.
Had a thought- what happens when you warm up the cloudy water? If it goes clear then it is probably a precipitant, if you heat it up and leave it a couple of hours and it goes cloudier I'd put money on bacteria. If it goes cloudier and then gets a green tints that's definitely algae.
If I was in the lab I'd put some samples on agar plates to see what grew and I'd check it under a microscope, under light microscopy algae are little cells and bacteria are teeny little specks which jitter about. But I don't expect you be able to do that.
If you work it out will you post the answer?