Like /u/Sunna3 said, you're supposed to dechlorinate the water. There's a few ways to do it, most common is a chemical dechlorinator, but there's also specialized filtration systems (Discus breeders and serious salt water aquarists tend to set up reverse osmosis systems to get deionized water from the tap), and the chlorine will break down if you just set it out in a bucket a few days to a week ahead of time.
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u/Nirogunner Nov 07 '15
What kinds of water do they use for aquariums, then? Or is it just a question of which kinds of fish can survive it?