When you say pool, do you mean swimming pool? If so, it probably has as much if not more chemicals than tap water.

If you mean garden pond, like with plants and fish, when you say pool then the water from that is probably just fine even if there are leaves in it. Actually pond water might even be a good source of bacteria rich stuff to get the bin going quickly.

The reason some might wish to avoid tap water is the chemicals will slow down the bacteria formation and can be hard on the worms too. If your tap water is well water, you are probably fine. If your water authority treats the water with just chlorine, then you can simply put the water in a bin or bucket for a few days before use and the chlorine will dissipate. If your water authority treats with chloramine, that is not so good since that stuff won't just go away and can even make baking bread difficult if you don't use filtered water.

Are you talking about actually taking water from your swimming pool, or just using rain water caught on the cover?

I'd think that taking water out of the pool itself would be a bad idea, the residual pool chemicals could be an issue, especially soon after chlorinating.

Rain water trapped on the cover should be fine though. The oak leaves shouldn't be a problem, as Worms happily eat damp oak leaves all the time.

I wouldn't be too worried about tap water in most areas - which would be in your swimming pool anyway. Obviously you can't beat natural rain water, but there must be a vast number of worm farmers, like me, who sprinkle tap water, without ever even giving it a thought. I think someone is being over cautious.

Here is a link that might be useful: working worms

Thank you tclynx; I probably should have been clearer on my "water source". It is rain water and snow that has melted and just laying on a heavy winter cover for the pool.
Thank you african; my remarks to "tclynx" pretty well cover the answers to your query. Thank you for the link to "working worms"
Both of your replies ease my mind about taking care of my soon to be worm stock.