I don't do Kefir, but I brew Kombucha. My tap water will destroy a scoby in a day or two.
If you can confirm that you have chlorine only - then you can just let the water sit overnight - and the chlorine will gas off - a little turbulence when setting that water aside or a hard stir occasionally will accelerate the process. Campden will also work (on both chlorine and chloramines) and do so relatively quickly, but I would also let that sit for a while before using, just to make sure the sulfur moves out of the water. You can use a half tablet for 5 gallons.
One other thing to consider is pH. There is a pH range that is optimal for bacterial growth and yeast growth. Do some reading on Kefir and see if you need to adjust hardness and/or pH to a specific level. Since yeast is involved - it will adjust the pH itself, but may take a while to re balance to the desired levels of other bacterium. I acidify my tea additions to below 5.4 with phosphoric acid before adding the sugars. I use RO water as my tap water is horrible.