The very water we drink, is not fit for our Koi by any means.
Mains water contains Chlorine and many hard metals, that just simply are not healthy, or productive for a healthy and balanced nitrogen cycle. In order to create a safe aquatic environment it becomes the main priority to ensure the water is dechlorinated at all times. Dechlorinating water can be done by two ways.
►Using a water purifying system
►Using liquid Dechlorinators