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Reverse Osmosis Systems

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Reverse osmosis is not a stronger filter. It is a different process, and understanding that difference is most of what a household needs before spending money on one. A conventional filter strains or adsorbs: particles too big to pass are caught, and dissolved organic compounds stick to carbon. Reverse osmosis pushes water under pressure through a semi-permeable membrane that passes water molecules and rejects most dissolved salts and minerals, concentrating them in a reject stream that goes to the drain.

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That makes it the right answer to a small number of genuinely difficult Australian water problems and the wrong answer to most of the common ones. If your supply is a bore with high salinity, or groundwater carrying dissolved minerals that no cartridge will touch, reverse osmosis is the domestic technology that addresses it. If your complaint is chlorine taste on a town supply, you are buying a desalination plant to solve a problem a carbon filter fixes for a fraction of the cost and without sending water down the drain.

The trade-offs are real and should be on the table before you buy: a reject stream that consumes water, which matters in a country that periodically imposes water restrictions; water so thoroughly stripped of minerals that many systems add a remineralising stage back in for taste; a slow production rate that requires a storage tank under the sink; and a drain connection that has to be made properly by a licensed plumber.

How a domestic reverse osmosis system actually works

  • A sediment pre-filter removes particles that would otherwise abrade or block the membrane, which is the stage that determines how long the expensive part lasts.
  • A carbon pre-filter removes chlorine, because chlorine damages the membrane material used in most domestic units on a town supply.
  • The membrane itself does the separation under mains or pump pressure, passing water and rejecting most dissolved salts to a concentrate stream.
  • A storage tank holds the product water, because the membrane produces slowly and nobody wants to wait at the tap.
  • A post-filter polishes the taste of water that has been sitting in the tank between uses.
  • Many systems add a remineralising cartridge, because water with almost everything removed tastes flat and can be aggressive to some plumbing materials.
  • A drain line carries the concentrate away, and it must be connected so there is no possibility of waste water being drawn back into the system.

When reverse osmosis is worth it, and when it is not

Reverse osmosis earns its place when the problem is dissolved. Salinity in bore water across large parts of inland Australia is the clearest example: it is not filterable in the ordinary sense, it makes water unpalatable long before it becomes a health question, and a membrane is the practical domestic answer. Hardness that leaves scale in kettles and on elements, and certain dissolved minerals that give water a metallic character, sit in the same category.

It does not earn its place when the problem is chlorine, sediment or general taste on a treated town supply. A carbon block cartridge solves that at a fraction of the purchase price, with no reject stream, no storage tank and a far simpler installation. Buying reverse osmosis for a chlorine complaint is the single most common overspend in this category, and it is usually the result of a sales process that never asked what the water actually contains.

The decision should follow a laboratory analysis of your supply, not a demonstration. If nobody has tested your water and told you what is in it, nobody can honestly tell you whether a membrane is the right tool.

System formats and Australian supply situations

  • Undersink systems with a dedicated tap are the standard domestic format, treating only drinking and cooking water and keeping the reject stream modest.
  • Benchtop units connect to a tap temporarily and suit renters, at the cost of a slower rate and a more awkward drain arrangement.
  • Whole-of-house reverse osmosis is rare in domestic Australia and expensive to run, but it appears on rural properties where a saline bore supplies everything.
  • Tank-fed properties usually need pre-treatment for turbidity and organics before a membrane is worth installing at all.
  • Bore-fed properties often need iron and manganese removed first, because those foul a membrane quickly and expensively.
  • Properties on a pressure pump rather than mains pressure may need a booster, since a membrane produces poorly at low inlet pressure.
  • Systems with a permeate pump reduce the amount of reject water produced, which is a meaningful consideration where water is scarce or carted.

The trade-offs and failure modes to plan for

  • The reject stream: every litre produced sends some water to the drain, which is an uncomfortable fact on a property under water restrictions or on carted water.
  • Slow production: the tank refills over hours, so a household that draws a lot at once will empty it and wait.
  • Flat taste, because water with most dissolved minerals removed is unfamiliar to drink, which is why remineralisation cartridges exist.
  • Membrane fouling from iron, manganese, hardness or turbidity that should have been removed upstream, which shortens membrane life dramatically.
  • A tank that loses its air charge, giving you a trickle at the tap and a system that looks like it has failed when it has not.
  • Pre-filters left unchanged, which is the most common reason an expensive membrane dies early.
  • Stagnation after a holiday, since water that has been sitting in a tank for weeks should be run off rather than drunk.

Certification, licensed installation and the drain connection

A reverse osmosis system is a plumbing product installed in a drinking water system, so the WaterMark Certification Scheme applies and installation is licensed plumbing work in every Australian state and territory. The dedicated tap is also a product in contact with drinking water, which brings it within the Australian Building Codes Board's lead requirement: NCC Volume Three limits lead in copper alloy plumbing products conveying drinking water to 0.25 per cent under Clause A5G4, with compliant products carrying the Lead Free WaterMark. The transition was extended in December 2025 and states and territories may adopt different dates, so ask your plumber what currently applies where you live.

The drain connection is the part of a reverse osmosis installation that is done badly most often, because it looks trivial. The concentrate line joins the waste system, and it must be arranged so that waste water can never be drawn back into the drinking water side. Backflow prevention is controlled by your water authority. A licensed plumber will know the requirement; a general handyman connecting the drain line into a sink tailpiece with a saddle clamp very often will not.

Looking after the membrane, which is the expensive part

  • Change the sediment and carbon pre-filters on the manufacturer's schedule; they exist to protect the membrane and skipping them is a false economy.
  • Expect the membrane itself to last considerably longer than the pre-filters, but only if those pre-filters have actually been maintained.
  • Check the storage tank's air pressure when flow at the tap drops, before assuming the membrane has failed.
  • Sanitise the system on the manufacturer's schedule, particularly the tank, since stored water is stored water.
  • Watch the ratio of production to reject; a system suddenly sending much more to drain is telling you something.
  • After any period away, run the tank off before drinking rather than consuming water that has been standing.
  • Keep a record of which cartridges suit the unit, because domestic reverse osmosis systems are far from standardised and the wrong cartridge fits badly.

Licensing and the paperwork to keep

As with any connection to the drinking water supply, installation is licensed work in every Australian state and territory, and the licensed job produces a compliance certificate under your own jurisdiction's scheme. Because plumbing regulation is a state and territory responsibility rather than a national one, the certificate's name and the notification process vary, and the right question to your plumber is simply which certificate you will receive and when.

Keep that certificate with the system documentation, the cartridge specifications and the installation date. Two things later depend on it: an insurance claim if the tank or a fitting fails under a kitchen bench, and the next technician's ability to work out what they are looking at. Reverse osmosis systems outlive the memory of who installed them more often than most plumbing.

Reverse Osmosis Systems: frequently asked questions

Is reverse osmosis worth it on Australian town water?

Usually not. Reticulated town supplies in Australia are treated and monitored, and the complaints households actually have about them — chlorine taste, occasional sediment after mains work — are what an activated carbon filter is designed to fix. Reverse osmosis addresses dissolved salts and minerals, which is a real problem on saline bore water and a non-problem on most town supplies. Buying a membrane system to solve a chlorine taste is the most common overspend in this category.

How much water does a reverse osmosis system waste?

Every system produces a reject or concentrate stream that carries the rejected salts to the drain, and the ratio varies substantially between designs. That is a genuine consideration in Australia, where water restrictions are periodic in many places and where rural households may be carting or tank-supplied. If the reject stream matters to you, ask specifically about the production-to-reject ratio of the model being quoted and whether a permeate pump is available for it, because systems differ considerably and the salesperson will rarely raise it unprompted.

Does reverse osmosis remove minerals I need, and does that matter?

It removes most dissolved minerals along with everything else, which is the point of the process. The dietary significance of minerals in drinking water is small compared with food, but the taste difference is immediate and noticeable, and water with almost everything stripped out tastes flat to most people. That is why many domestic systems include a remineralising cartridge as a final stage. If taste matters to your household, ask whether the system quoted includes one and what it costs to maintain.

Can reverse osmosis make bore water safe to drink?

It can address salinity and many dissolved contaminants, but it is not a complete answer on its own and it should never be installed on an untested bore. The right sequence is a laboratory analysis first, then a treatment design that puts the right stages in the right order, with disinfection considered separately because a membrane is not a disinfection device. Bore water also commonly carries iron, manganese and hardness that will foul a membrane quickly if they are not removed upstream, so pre-treatment is usually part of the answer.

Why is my reverse osmosis tap suddenly just trickling?

The first thing to check is the storage tank's air charge, not the membrane. A domestic system produces slowly and stores what it makes in a pressurised tank; if that tank loses its air pressure, the water is still there but there is nothing to push it out, and you get a trickle. Blocked pre-filters are the other common cause, and they are the cheaper one to rule out. A failed membrane is further down the list, and a technician should check the simple things before quoting you for the expensive part.

Sources

  1. NCC: Update on the transition to lead free plumbing products

Written by the LokalMatch editorial team. Last reviewed 22 September 2026. How we write and check our guides

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What affects the cost of reverse osmosis system

Prices depend on the details of your project. We only publish price ranges when they’re backed by real LokalMatch quote data or reliable sources. Until then, here’s what usually changes the price:

  • Type of problem and how easy it is to find
  • Access to pipes behind walls, under floors or underground
  • Parts and fixtures chosen
  • Age and material of the existing pipes
  • Emergency, evening or weekend service
  • Permits and inspections, where required

How to compare water treatment specialists before you hire

  • Hire a plumber who is licensed for this work in your area, especially for gas water heaters, sewer lines and new plumbing.
  • Ask whether they charge a flat rate or by the hour, and what the call-out fee covers.
  • For leaks and drain problems, choose someone who explains the cause and doesn't only clear the symptom.
  • Get the scope in writing for larger jobs such as a water heater, sewer repair or re-piping.
  • If it's urgent, ask how soon they can arrive and whether after-hours rates apply.

Questions to ask water treatment specialists before you hire

  • Are you licensed for plumbing work in my area?
  • Do you charge a flat rate or by the hour, and is there a call-out fee?
  • What do you think is causing the problem?
  • Will this work need a permit or an inspection, and who will arrange it?
  • Will you need to open walls, floors or the yard to reach the problem?
  • What warranty do you offer on parts and labour?

When to call a pro for reverse osmosis system

  • An active leak: shut off the main water valve if you can reach it safely, then call a plumber.
  • Sewage backing up into drains or the basement
  • No hot water, or water pooling around the water heater
  • Pipes that may have frozen during a cold snap

Reverse osmosis system permits and local rules

Some reverse osmosis system work needs a permit or has to meet local bylaws. Rules vary by municipality, so ask your pro whether a permit is needed and who will apply for it — and check with your city or town if you’re unsure.

Permits and licensing

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