RO installation: how a reverse osmosis system goes in

Advertised prices, verified

The RO install, step by step

1. Shut off the cold supply and tee in the feed. Close the cold angle stop under the sink and fit the feed adapter or valve the kit supplies. This small valve is the system's water source, so make the connection on the cold line only: hot water damages membranes and housings.
2. Mount the manifold and set the tank. Hang the filter manifold on the cabinet wall high enough to swing the housing wrench underneath, and stand the storage tank where it will not block the trap. Dry-fit everything before fixing, because cramped cabinets punish poor planning.
3. Connect the drain line properly. The reject line connects to the drain above the trap, either through a drain saddle clamped to the tailpiece or an air-gap faucet where local code requires one. Route it without loops or kinks, since a strained drain line is the usual cause of a noisy system.
4. Fit the faucet, pressurize and flush. Drop the RO faucet through the sink's spare hole or a newly drilled one, connect the tubing per the color coding, then open the feed and check every fitting. Flush the first tankfuls to drain on the printed schedule before anyone drinks from it.

What decides whether to DIY or hire

The kits are genuinely designed for homeowners: push-fit connections, color-coded tubing and no soldering anywhere. If your sink already has a spare hole for the faucet and your drain is accessible, there is little a plumber does that you cannot. Our under sink reverse osmosis system installation guide walks the cabinet work in detail.

Hire it out when the job grows: drilling granite or stone for the faucet, adding a pressure-boost pump for low-pressure homes, tying the RO line to a fridge across the kitchen, or any whole-house RO project with its pump, storage and repressurization equipment. Those are jobs where experience saves the countertop.

Costs beyond the box

The table above shows the vendors' published system prices, and for most under-sink installs that is nearly the whole cost if you fit it yourself. Add a drill bit if the sink needs a new hole, and possibly an air-gap faucet where code demands it.

Budget for the running cost from day one: replacement pre-filters on their printed schedule and the membrane when output falls. A cheap system with expensive proprietary cartridges can cost more over a few years than a better system with standard-size filters.

Common questions

How long does an RO installation take?

A first-time homeowner install of an under-sink system typically takes an afternoon including the initial flush. A plumber who fits them regularly is done in an hour or two, plus the flush time.

Does an RO system need electricity?

Standard under-sink systems run on water pressure alone. Pumped systems for low-pressure homes, tankless models and UV-equipped units need an outlet in or near the cabinet, which is worth checking before you buy.

Where does the reject water go?

To the drain, through a connection above the trap. Every RO system sends a stream of concentrate to waste while it makes purified water; that is inherent to how the membrane works, not a fault in the install.

Can RO be installed on well water?

Yes, and it is common, but the feed water needs to be pre-treated first: sediment, iron and hardness all shorten membrane life. Test the well and fix upstream problems before the RO goes in.

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