What I don't understand is that they dumped black balls in the reservoir. If you want to keep the water cool to lessen evaporation wouldn't it make sense to use white or reflecting balls so the water stays slightly cooler?
I would be glad to know why black balls are chosen.
According to a chemist on /r/askscience, the plastics probably contain carbon black [0] as a UV protectant. So it might not be deliberate.
(/u/Platypuskeeper) Although I have not seen a specification of what
the balls are made of, what I know from polymer chemistry is that the
black is quite likely from carbon black (essentially soot), which is
used as an additive/filler in polymers (e.g. tire rubber) for multiple
reasons but not least UV protection. Carbon black is one of the most
(if not the most) effective UV-protective additives, precisely because
it absorbs the UV and prevents it from penetrating deeply into the
plastic. Plastic without some UV protective additive would degrade
pretty quickly in the California sun, not least HDPE which has pretty
bad UV resistance.
Black absorbs more light (and, yes, heat), which means less light penetrates through it to heat the water directly. If you block one bright light with a sheet of thin white plastic, and another with a sheet of thin black plastic, you'll see a lot more light shining through the former. And do remember that the primary purpose is to block UV, not heat, so you want maximum light absorption even if it means greater heat transfer.
Chrome-mirrored balls would certainly be even better, but the whole reason they're using plastic balls is because they're dirt cheap. If you have enough money to fill your reservoir with disco balls, you'd be better off just building a gigantic awning.
The primary purpose of these is not to slow down evaporation. In fact they have a negligible effect on the rate of evaporation.
Their primary purpose is to absorb the light spectra that drives chemical reactions in the treated water to prevent carcinogenic bromate from being formed.
Most of the reporting on this, including this article, is pretty bad, and causing a lot of laymen to ask questions like yours, because it doesn't make sense as described in the reporting.
Now you just said the opposite of what intuition suggests without any evidence, or even argument. Please elaborate and don't just heat up the discussion!
Does that look like an explanation to you? I don't see anything about black. I don't see anything about white. I don't see anything about reflecting materials. I see something from chemistry, maybe?
Customer: "Why should I buy the product?" Developer: "Here we had a problem with the inheritance tree. We worked around it with a factory method."
I would be glad to know why black balls are chosen.