Water Treatment · Service

Reverse osmosis, for one tap, done properly

An under-sink RO system gives you excellent drinking water at the kitchen tap and does absolutely nothing for your shower, your laundry or your water heater. Understanding that is most of the decision.

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In short

What is reverse osmosis installation?

Reverse osmosis pushes water through a semi-permeable membrane that lets water molecules pass and rejects most of what is dissolved in it, sending that concentrate down the drain. In a house it almost always lives under the kitchen sink, feeding a dedicated faucet and often the fridge, with a small pressurised tank storing treated water so you are not waiting on the membrane. It is point-of-use by nature: excellent for what you drink and cook with, irrelevant to everything else in the building.

Triggers

Signs you need reverse osmosis installation

You are buying bottled water for drinking and cooking and would rather not
Your tap water tastes or smells wrong even though the utility report is unremarkable
A lab result flagged something you want addressed specifically in your drinking water
You have a softener and want an unsoftened-tasting drinking supply back at one tap
The ice maker and the water dispenser in the fridge are producing ice you can taste
You are on a private well with a treatment train handling the house but nothing polishing the drinking supply
You want an aquarium, a coffee setup or a steam oven fed with consistently low-mineral water

Seeing something not on this list? Browse water treatment problems by symptom →

The job

How reverse osmosis installation actually works

Confirm RO is aimed at the right problem

RO is a drinking-water technology. If your issue is scale on the heating elements or soap that will not lather, RO under one sink will not touch it. Match the technology to where the complaint physically occurs before anything else.

Watch for: Being sold RO as a whole-house answer. Whole-house RO exists but is an entirely different scale of equipment and cost, and it is very rarely the right domestic answer.
Check incoming pressure — the membrane depends on it

Reverse osmosis is driven by pressure across the membrane. Low supply pressure means slow production, a tank that never fills properly, and poorer performance. Where pressure is genuinely low, a booster pump is the fix and it should be specified up front.

Watch for: Nobody measuring pressure before quoting, especially on well systems where the pressure tank's cut-in point governs the low end of the range. This is the most common cause of a new RO system that "does not seem to work".
Understand the stages, and that the membrane is not the only consumable

A typical unit runs sediment and carbon pre-filters, then the membrane, then a post-filter polishing the taste on the way to the tap. The pre-filters exist mainly to protect the membrane — chlorine in particular damages some membrane types, which is why the carbon stage is not optional.

Watch for: A quote that prices the system but is vague about the replacement schedule. Pre-filters are changed far more often than the membrane, and skipping them is how an expensive membrane dies early.
Accept the wastewater, and ask what the ratio is

Every RO system sends concentrate to the drain — that is how it works, not a defect. The ratio of drain water to product water varies substantially between designs, and newer units are markedly better than older ones. Ask for the figure for the specific model.

Watch for: A seller who will not state the ratio, or who claims there is no wastewater at all. On a septic system or a metered supply, this figure is worth asking about specifically.
Site the tank, and understand what it does to flow

The membrane produces slowly, so a small pressurised storage tank holds treated water ready for use. That tank is why the RO faucet delivers a usable stream rather than a trickle, and it is also why the flow is gentler than your main tap and slows as the tank empties.

Watch for: A tank with lost air pre-charge. It is the most common cause of an RO system that gives you half a glass and then dribbles, it is cheap to re-pressurise, and it is frequently misdiagnosed as a dead membrane.
Drill the faucet hole — the irreversible step

RO needs its own small faucet, usually in a spare sink knockout or a new hole in the sink deck or worktop. Stainless is drillable with care; granite, quartz and composite need the right bit and a steady hand; some materials are genuinely risky to drill.

Watch for: Someone drilling an engineered stone worktop without saying out loud that a mistake here is not repairable. If there is no spare knockout, agree the exact position and the method before the drill comes out, and consider an air-gap faucet variant if your local rules call for one.
Make the drain connection properly

The concentrate line ties into the sink drain, traditionally via a saddle clamp on the waste pipe above the trap. It must go in above the trap and be arranged so nothing can siphon back, and in some jurisdictions an air-gap faucet is required rather than optional.

Watch for: A drain saddle clamped below the trap, or fitted to a pipe material it was not made for. This is the part of an RO install that DIY guides gloss over and that inspectors look at.
Decide on the fridge line and remineralisation

Running RO water to the fridge is popular and straightforward, but the long run means slower recovery and it is worth checking the appliance is happy with the supply. Some people add a remineralisation stage to put a little mineral content back, mainly for taste — RO water strikes many drinkers as flat.

Watch for: Assuming remineralisation is a health necessity. It is largely a taste and, for some, a corrosivity consideration. Sellers on both sides overstate their case; if the flat taste bothers you, add it, and if it does not, do not.

Money

What does reverse osmosis installation cost?

Under-sink reverse osmosis typically runs from a couple of hundred dollars for a self-installed unit to roughly a thousand or more professionally installed with a fridge tie-in, a booster pump or an air-gap faucet. Ongoing cost is pre-filters changed regularly and the membrane much less often. Ask for the replacement schedule and prices.

See the full reverse osmosis installation cost guide — by material, size and region →

Straight answer

When reverse osmosis installation is the wrong call

Everyone else ranking for this is paid when you say yes. Here's when you shouldn't.

You want your showers, laundry or appliances improved. An under-sink unit treats one tap. Your shower, your washing machine and your water heater will be exactly as they were the day before. If those are the complaint, the treatment has to happen where the water enters the building — see whole-house filtration.
You expect it to replace a softener. It does not. RO will produce lovely drinking water in a house that still scales up every kettle, heater and shower screen, because the hardness is untouched everywhere except that one faucet. The two are complements — see softener installation.
Your water may be microbiologically unsafe and nothing is disinfecting it. Do not treat an RO membrane as a barrier against a bacteria problem you have not addressed properly. That is a health-department conversation and a disinfection question — see UV sterilisation.
Your supply pressure is low and no booster is in the quote. You will get a system that produces slowly, stores badly and disappoints daily. Measure first; the pump is much cheaper as part of the original install than as a callback.
Nobody can tell you where the drain connection is going. The drain tie-in and the faucet hole are the two parts of this job that are hard to undo. If the answer is vague at quoting stage, it will be improvised on the day.
You will not change the pre-filters. RO is the least forgiving common system about neglected consumables — spent carbon stops protecting the membrane, and the membrane is the expensive part. If a calendar reminder is not going to happen, buy something simpler.

Your options

Types of reverse osmosis installation

Standard under-sink RO

Pre-filters, membrane, post-filter, storage tank, dedicated faucet. The default domestic configuration.

Tankless / on-demand RO

No storage tank — produces on demand using a pump. Saves cabinet space; depends more on electrics and pressure.

RO with remineralisation

Adds a stage that returns some mineral content, mostly for taste. Optional, not a health requirement.

Whole-house filtration

What you need if the problem is not confined to the drinking tap.

Softener plus RO

The common pairing: softener for the building, RO for the glass.

Compare water treatment options side by side →

Straight answer

Can I do this myself?

The drain saddle must connect above the trap. Below it, or arranged so waste can siphon back toward the unit, and you have built a cross-connection into the appliance you drink from. This is the detail most consumer install videos skate over.

Reasonable to DIY

Changing pre-filter and post-filter cartridges on schedule
Sanitising the housings when you change cartridges, following the manufacturer's instructions
Checking and restoring the storage tank's air pre-charge with a tyre gauge and a pump
Fitting a complete kit under a sink that already has a spare faucet knockout and a compatible drain arrangement

Call a licensed pro

Drilling a new faucet hole in granite, quartz or any composite worktop
Making the drain connection where the waste arrangement is not straightforward, or where local rules require an air-gap faucet
Adding a booster pump, or any work on a well pressure tank to support the system
Tying into a fridge line that runs through cabinetry or a wall

Before you sign

What to check when hiring for reverse osmosis installation

What is my incoming pressure, and does this system need a booster at that pressure?

The single best predictor of whether you will be happy with the system. It should be measured, not assumed.
What is the drain-to-product water ratio for this specific model?

Ratios vary widely between designs. It matters most on metered supplies and septic systems, and a straight answer indicates the seller knows the product.
Where exactly is the faucet hole going, and what is the plan if the material chips?

This is the irreversible part. Agree position and method before anyone touches a worktop with a drill.
How is the drain being connected, and do local rules here require an air-gap faucet?

It is the cross-connection question, and requirements genuinely vary by jurisdiction. Ask before install day, not during.
What is the filter and membrane replacement schedule, and what do the parts cost?

Consumables dominate the lifetime cost of RO, and proprietary cartridges can cost several times the generic equivalent.
Which specific certifications does this unit hold, and for what?

Certification is contaminant-specific. A unit certified for taste and odour is not thereby certified for anything else, and a claim with no standard named beside it is marketing.
Are you running a line to the fridge, and does the appliance manufacturer accept RO water?

Usually fine, occasionally not, and much easier to establish before the cabinet is opened up than after.

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Local pros

Reverse Osmosis Installation near you

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Related work

Often done at the same time

Whole House Water Filtration

When one tap is not enough

Water Softener Installation

The usual partner system

Lead & PFAS Filtration

When certification for a specific contaminant is the point

Water Testing

Establish what you are actually treating

All water treatment services →

FAQ

Reverse Osmosis Installation — questions people ask

Still have a question? Talk to our team →

Does reverse osmosis waste a lot of water?

It sends some water to the drain as concentrate — that is the mechanism, not a fault — and how much varies a great deal between designs. Newer units are considerably more efficient than the reputation the technology carries from older equipment. Ask for the specific ratio of the model you are quoted, and weigh it against what you are currently spending on bottled water.

Is RO water unhealthy because it removes minerals?

The mineral content of drinking water is a small contributor compared with food for most people, and this argument is pushed hardest by people selling remineralisation stages. What is uncontroversial is that many drinkers find RO water tastes flat, and a remineralisation stage fixes that. If you have a specific health reason to care, ask a doctor rather than an installer.

Why is my RO faucet only giving me half a glass?

Most often the storage tank has lost its air pre-charge, so it holds much less than it should. It is checked with a tyre gauge at the tank valve with the tank drained and corrected with a bicycle pump — a ten-minute job. Other candidates are clogged pre-filters, low supply pressure, or a closed tank valve. A dead membrane is usually the last thing on the list, not the first.

Can I connect reverse osmosis to my fridge and ice maker?

Yes, and it is one of the most appreciated parts of the install because it changes how ice tastes. Two practicalities: the longer run means the tank recovers more slowly if you are drawing heavily, and it is worth checking the appliance manufacturer is content with an RO supply. Both are easier to sort before the cabinet is opened.

Do I need a softener as well as RO?

If you have hard water and it is bothering you anywhere other than the drinking tap, yes — they solve different problems in different places. There is also a practical argument the other way round: feeding an RO system pre-softened water reduces scaling on the membrane, so on hard water the pair genuinely helps each other.

How long does an RO system take to install?

A straightforward under-sink fit into an existing knockout is usually a few hours. Drilling a new faucet hole in a stone worktop, adding a booster pump, or running a line across to the fridge each add meaningfully to that. If nothing awkward is discovered, it is a same-day job.