I'm not sure the chems being sold to treat tap water is sufficient these days. Back 1-2 years ago, my city water started adding chloramines to the water supply--they were nice enough to send out warnings a few months before doing it warning that it will affect aquatic pets. I started using Amquel+ to all the fish water, letting is sit at least a whole day (sometimes longer if I didn't need all the bottles of water immediately)--even though the stuff made the water stink like sulfur bigtime. However, even with this stuff, everything including plants, snails, shrimp, fish started dying. I switched to using Jungle's Ammonia Chloramine Eliminator (ACE) but the dying continued, tried Prime but the same. Finally, out of desperation, I started buying mass quantities of Crystal Geyser Spring bottle water and everyone has been doing fine (except me, not only is this costly but I have to lug the stuff home). I have sense figured out I can also use Alhambra spring water or Alhambra Crystal (something or other treated water), or Arrowhead spring water. I don't treat any of the bottled spring water with chems since I investigated their water purity stats and it could be used without further treatment by me. I'm afraid more and more USA water is going to become like this, so loaded with purification chemicals it can't be consumed safely by anyone.
When you choose a brand of bottle water, choose one that is probably going to be available to you always and easily since different companies do different things to their water and any change may be bad for your fish. Test out any new water (small container, put in a fish, if it doesn't react badly the water is safe to use) and then continue to use that brand of water. Spring water is better than treated drinking water (which is basically just tap water that has been filtered and/or chemically treated to remove excess products).
EVERYONE, before you buy any more fish, buy yourself test kits. They last a long time and if you are going to keep fish, YOU NEED TEST KITS. I don't use mine often but when the fish start acting odd or if something smells off to me or if I set up a new tank, etc., I run the tests so I can rule out that possibility (or fix whatever might be wrong--the things the test kits test for are all relatively easy to correct). Don't get the test strips since they don't come with expiration dates and you never can tell how long they have been sitting around in storage (old test strips will give you false readings).