I had a RO/DI unit with a faucet adaptor - you simply unscrew the old aerator on a faucet tip and replace with one that has a ridge in it (comes as part of the faucet adaptor). It works like a regular faucet aerator. However, when you need RO/DI water, the intake tube from the RO unit "snaps on" to the ridge of the adaptor (takes a second), and when you're done you pres a button or two and it "snaps off" (takes a second). No modifying plumbing whatsoever unless unscrewing an aerator and screwing a new one on once counts. It's about as difficult as adding a kitchen sink faucet water purifier like Pur or Brita (extremely easy, even for someone as mechanically disinclined as myself, and that's saying something!).