Dangers of cultivating tap water "starter"?

Hi, here I am living in Florida with the bad tap water. (In comparison, when I visited New York City from Upstate New York I complained about the bad, over processed tap water only to be told that NYC was known for its good tasting tap water, and Floridas tap water is even worse.)

And I noticed that when I let tap water set for several days, it usually acquires a slightly burnt taste, which I can only assume is from algae starting to grow in it. It worsens the taste, if that’s possible.

But I noticed that now, the water I let set over the past couple days has acquired a really good taste, very natural, sort of like a mountain stream.

I haven’t let this water bottle get empty and have been filling it only halfway for the past few days and luckily it hasn’t changed from its fresh flavor. I’m thinking of using this water to “Seed” other water bottles.

I’m thinking I should at least nuke the bottles (after I have let them set for a couple days.) If I do that it shouldn’t be dangerous except for botulism, right? but I’m wondering if that would kill the taste, too.

I’ve never tasted it, but we were advised to let the water we give our pet toads sit out for a day or so. Apparently this allows the cholorine to break down and go away. We keep it in a gallon plastic bottle and, although it never gets quite empty, it never grows anything either.