hummingbird sugar water

For years I've always boiled tap water for 1 minute, then added the sugar, then let completely cool off before filling the feeders.   Since the cool off time could take an hour, I have tried something I read which is to only boil half the water so that the sugar can fully dissolve, then adding cool tap water for the remainder.  This was very easy and cut out the cool off time completely...but the birds don't seem to like the sugar water now.  What could that taste differently...could the cool tap water have too much chlorine taste?