Being a long-time pool owner and maintainer, (and quite good at it), I can assure you that the water in MY pool, at least, is chemically FAR more pure than tap water that's 'safe' to drink. After getting the pool resurfaced a few years ago and refilling it with city water, it was quite amusing (Scary, actually) to see the yellowish tint, the cloudiness, and the alarming chemical balance. After a solid week of daily treatment and filter backwashing, the water began to return to the standard quality I expect, which is clear enough that you can distinguish between a dime and a nickel at the bottom of the pool as well as you can with them lying on the ground. You can read the date on a dime at the bottom of the pool from the same distance as you can with it on the ground as well.
If you want to give your pool chemical seller a hard-on, take a sample of tap water to him, have it analyzed, and ask him to sell you what you need to treat it. It'd be one or two of just about everything.
The water in my pool is so clean that I prefer to use it when making coffee or tea. The flavor of the product is MUCH better, and you need less sugar to get the same apparent sweetness.
If you're going to rely on a pool as an expedient source for drinking water, drop a dime into it. If you can tell it's a dime on the bottom of the pool, it's passed test 1. Next, get down with your nose right at the water level and smell it. If the odor is not objectionable and is very faint, you can be pretty sure it's MUCH cleaner than most city water. Taste test it as well. You'll know something's wrong if it has a metallic taste. That would probably be copper in the water.
CJ