Installing an RO system under a kitchen sink is a half day of careful work rather than a plumbing project, but it touches four things at once: the cold supply, the drain, the countertop or sink deck, and the cabinet space. Almost every problem people report afterward traces back to a decision made in the first hour, so the fit checks matter more than the wrench work.
Fit checks before you open the box
Confirm five things. There is cabinet space for the filter manifold on the wall and the storage tank standing upright, with room to change cartridges without emptying the cupboard. There is a spare hole in the sink deck or countertop for the dedicated faucet, or you are prepared to drill one. The cold supply has an accessible angle stop to tee off. The drain has a horizontal or vertical section above the trap that a drain connection can be fitted to, ideally not on the disposal side. And your local code's position on air gap faucets is known, because that decides which faucet and which hole size you need.
The install sequence
Work in an order that keeps the awkward jobs first. Mount the faucet in the sink deck and tighten it from below before the cabinet fills up. Fit the drain connection next, above the trap, following the maker's instructions on orientation so waste cannot sit in the fitting. Then fit the feed adapter to the cold angle stop, mount the filter manifold to the cabinet side, and place the tank where its valve stays reachable. Connect the tubing last, cutting each run square, seating it fully into every quick connect and leaving gentle bends rather than kinks. Keep the color coding, since it is the only labeling you will have in two years.
Startup, flushing and proof
Open the feed valve slowly and check every joint before opening the tank valve. New carbon media and a preserved membrane both need flushing: the manufacturer will specify filling and dumping the tank a number of times before the water is used, and skipping it is why some new systems taste odd or dispense gray water. Once flushed, run the faucet and confirm a steady stream, then check the system with a total dissolved solids meter if you have one, comparing the feed water against the product water. Come back a day later and inspect every fitting again, because slow leaks announce themselves overnight.
The mistakes that cause callbacks
Five recur constantly. Tubing not pushed fully home in a quick connect, which holds pressure for hours and then releases. A drain connection fitted on the disposal side or below the trap, which sends waste back toward the fitting. The feed teed into the hot supply, an easy error under a crowded sink. The tank valve left closed after commissioning, producing a system that dispenses a trickle and stops. And a membrane installed without its prefilters flushed first, which shortens its life for no reason. Each is trivial to avoid and irritating to diagnose afterward.
When to hire it out
Drilling stone, quartz or fireclay for a faucet hole is the most common reason to bring in a professional, since the wrong bit or the wrong technique cracks an expensive surface. A cabinet with no accessible drain point, a local code requiring an air gap you would rather not fight with, or a sink area already crowded by a disposal and a filtered water line are the others. Fitting the system to feed a refrigerator adds a longer tubing run and a pressure question worth checking against the fridge manual. Our RO system installation page covers what a professional install should include and what a fair quote itemizes.
Questions people ask about installing ro system
How long does an RO installation take?
A straightforward under-sink install with an existing faucet hole is commonly a couple of hours plus flushing time. Drilling a countertop, working around a disposal or fitting an air gap faucet extends it, and the flush cycles run afterward regardless.
Do I need an air gap faucet?
That depends on your local plumbing code, which some jurisdictions apply to RO drain connections and others do not. Check before buying the faucet, since air gap models need a larger mounting hole and behave differently from standard ones.
Can I install an RO system without drilling the sink?
Yes if there is a spare hole under a soap dispenser or sprayer blank. If not, a countertop RO unit avoids drilling entirely at the cost of counter space and a reservoir you fill by hand.
Why is my new RO system producing so slowly?
Check the tank valve is fully open, the feed valve is fully open, no tubing is kinked, and the tank has its factory air charge. Low household pressure also slows production, which is what booster pumps exist to correct.