The RO-3500 is a very good reverse osmosis drinking water system.
http://www.waterfilters.net/culligan/reverse-osmosis/US-Filter-RO-3500.htm
You can "T" off the line from the above system to the faucet so you can have another line going to your insta hot system. It would just require a plumbing "T" fitting.
Thank you,
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