The problem is that the chlorine in the water probably combined with wort constituents to form chlorophenols, which have a much lower flavor and aroma threshold than straight chlorine. So even if you can't smell or taste the chlorine in the water, it can create noticeable amounts of chlorophenols which can smell like bleachy sanitizer.
Invest in some campden tablets, it's a cheap way to make sure it doesn't happen again.