A reverse osmosis system pours through its own small faucet, and that faucet needs a mounting hole of its own. If the sink has no spare sprayer or soap dispenser hole, someone has to drill the sink deck or countertop. Stainless is a careful DIY job. Granite and quartz are better left to a pro.
Why can't the RO water come out of my regular faucet?
An RO system sends treated water up a dedicated line to a dedicated faucet. The standard setup is a separate spout, and the systems in the manuals cited here each ship with their own faucet. Our page on what to expect when a reverse osmosis system is installed walks through the whole job, and this question is one step of it.
The spout mounts the way a soap dispenser does: a stem drops through a hole, and a nut and washer lock it from underneath. No hole, no mount.
What are my options when there is no spare hole?
Check these in order, because the first is the easiest.
- 1Use an existing hole. Springwell's guide says it plainly: "If your sink has an existing sink sprayer or soap dispenser hole, you can use it for the faucet installation." Perfect Water's Home Master manual says the same: "Use existing hole, or drill 1” hole in sink top." Many sinks ship with a sprayer hole or a dispenser hole under a cover plate, so lift the plate and look before you pick up a drill.
- 2Pick a different spot. A deck-mount pre-punched for a side spray or soap dispenser is often free if the old sprayer was removed years ago. The same manual lists a 1-inch hole saw or masonry bit as the tool when no hole is available, and its hole saw is "not required if sink has a pre-drilled hole."
- 3Drill a new hole. Springwell puts it this way: "If not, you'll need to drill a hole in the sink top or the countertop next to the sink." The size comes from your system's manual. Perfect Water's Home Master manual calls for a 1-inch hole, so do not assume the hole is a half inch.
Why is drilling the part people worry about?
The risk is to the sink or counter, not the plumbing. The material decides how it goes.
- Stainless steel. The most forgiving, but the sink is still thin metal and a bit can wander, so mark the center and drill slowly with the bit square to the sink.
- Porcelain or enamel. It chips. Perfect Water's manual calls for a 1-inch masonry bit, drilling slowly with the bit perpendicular to the sink, and rinsing the bit tip and sink area with cool water for every 20 seconds of drilling. It also warns that "Small localized flaking or chipping may occur."
- Granite, quartz and other stone. Springwell is direct about it: "If your countertop is made of granite, quartz, or another material that is prone to splitting, it is generally recommended to have a certified professional drill the faucet hole."
Perfect Water's warning applies to all of them: serious cracking and damage may occur to your sink even if instructions are followed exactly, because of age and imperfections inherent in natural materials. A sink or slab can't be un-drilled. That is why a hole you can reuse beats a new one.
Where should the new hole go?
Pick the spot before you mark it. Perfect Water and Springwell point to the same checks:
- Look underneath first. Perfect Water says to check the underside of the sink for spacing from trim, curvatures and other obstacles, and to leave enough room under the sink to use hand tools.
- Room for the nut and tubing. Pick a spot where you can still reach the faucet stud from below once the hole is done.
- Where the water falls. Pick a spot where the spout reaches over the sink basin.
Springwell adds that the opening shouldn't interfere with anything beneath the sink and that there must be enough room for the connections.
Does an air gap change the hole?
It can. Springwell notes that on faucets with an air gap, you route the brine tubes through the installation hole first and attach them to the faucet base. Some local plumbing authorities require that air gap, so follow your local plumbing code. We cover that in the air gap faucet for RO systems, and the same idea is behind the dishwasher air gap. Check your system's manual for the hole size before you buy a bit.
Should I drill it myself or hire it out?
Do it yourself only if the sink is stainless steel or you already have the exact bit for the material, you can see the underside clearly, and you are comfortable losing the sink if it goes wrong. Hire it out for stone, quartz, an undermount sink with no deck beside it, or a countertop you plan to keep for years. If you are weighing sink materials anyway, the best material for a kitchen sink covers how each one wears.
If you are not sure what your sink is made of or whether a hole is free, HQ Plumbing and Air is licensed and insured and gives free estimates with upfront pricing, so you can get a look at the sink before anyone drills. See our water treatment and softening page.