I use a Woder under sink system. It was easy to install, easy to change the filters, and they last a long time. All the cold water at the kitchen sink runs through it. There is no separate faucet. It cuts the cold water flow rate down a bit, but it still much greater than one of the systems with a separate faucet.
https://woder.com/products/wd-g4-dc/
Seems like it would be easy to add a T so this could be plumbed to a separate tap if desired.
Yes if you wanted, but I prefer a less cluttered counter top.
One thing to keep in mind is that these systems produce about 3 gallons of waste water for ever gallon of purified water. When installed under a sink, the waste line goes directly into the drain. I find that wasteful, so I installed mine next to the washer. I put the drain line directly into the washer to fill the tub for laundry, or I fill jugs and use that water for general cleaning where high mineral content isn't a concern. It's a bit unsightly (as is the condition of my laundry room), but no one sees it.
A permeate pump can be added to a ro system to increases the efficiency and reduce the amount of waste water.
This (link below) seems to explain it well although in the UK were the tap water is considered very good to current internationally standards I still think the brine would be considered a waste by most, so for now a carbon gravity system looks to be my favoured solution (also no power required).
It does make me wonder why reverse Osmosis systems don’t push the permate pump as a standard solution. Maybe size, running costs or not wishing to highlight the increased water use?
https://www.purewaterproducts.com/articles/how-permeate-pumps-work
‘’The brine performs the essential function of carrying away the impurities and keeping the membrane clean. It isn't “wasted” any more than the water you wash your hair or mop your floor with is wasted”
So a quick update......been very happy with the system but it leaves in too much calcium (yes I know it is good for you) and the kettle and pots are suffering
Interesting! We must not have as much in our water supply, as I haven't noticed that issue at all.
