I have used "city water" in my pond "fish tanks" with no obvious ill effects.

Assuming normal chlorination levels, much of the chlorine should have evaporated out of the city water within the first 24 hours of holding it in a container or pit open to atmosphere and sunlight. If you could leave it 4-5 days, then essentially 100% of the chlorine would be gone from the water.

Also, if you could aerate the water in the container to continually move the bottom water up to the atmosphere interface, then the chlorine would be cleared much more rapidly.

Sorry to hear about your fish!