Reverse Osmosis Systems near you

Reverse osmosis sits at the tight end of a family of membrane processes. The DWI's treatment guidance describes membrane pore sizes for reverse osmosis as less than 0.002 micrometres, with operating pressures ranging from 15 to 50 bar in the general case, and notes that the process produces a treated water stream and a relatively concentrated waste stream. For comparison, the same guidance puts nanofiltration at roughly 0.001 to 0.01 micrometres at around 5 bar, ultrafiltration at 0.002 to 0.03 micrometres below 5 bar, and microfiltration at 0.01 to 12 micrometres at 1 to 2 bar.

That pressure range explains most of the practical problems. Domestic packaged units are built to run at mains pressure rather than at industrial figures, but they still want good, steady incoming pressure, and a property at the end of a long or undersized supply pipe may need a booster before an RO unit will produce water at a sensible rate. It also explains the storage tank: because production is slow, the unit fills a small pressurised vessel between uses so that the dedicated tap delivers a normal flow.

The DWI notes that reverse osmosis has the advantage that packaged point-of-use systems are available which can be used without any modifications, which is why domestic RO is nearly always an under-sink unit with its own tap rather than something treating the whole house. It also records the most common application of reverse osmosis as desalination of sea water, with use for nitrate removal having been proposed — a reminder of the scale the technology was built for.

The Inspectorate defines point of use treatment as the process by which water is made wholesome at designated points within a premises, as distinct from whole supply treatment, which provides wholesome water at all points of consumption. Its stated preference is unambiguous: it advises whole supply treatment in preference to point of use wherever possible, and without exception where a private water supply is being used as part of a commercial or public activity.

The reason it gives is the gap a point of use device leaves behind. Despite the financial benefits of treating only one outlet, the Inspectorate warns that this arrangement may present uncontrolled risks at taps where there is no point of use treatment — the bathroom basin a child drinks from, the outside tap someone fills a kettle at, the utility room sink. It also states that installing a point of use device must not compromise human health at any point on a supply where the water is used for one or more domestic purpose.

The Inspectorate adds that suitability must always be determined on a case-by-case risk basis, taking account of the vulnerability of those likely to use it. For a household on mains water installing RO for taste at one tap, none of this is alarming. For a household on a private supply relying on an RO tap to make a contaminated source drinkable, it is the central objection to the whole arrangement.

This is the most important safety point about domestic reverse osmosis and the one least likely to appear in a sales brochure. Membrane processes in a private water supply, the DWI says, should not be relied upon as the sole means of disinfection, because of the inability to verify membrane integrity. A pinhole in a membrane does not announce itself, there is no household instrument that detects it, and the water on the far side looks and tastes exactly the same.

That has a direct consequence for anyone drawing from a borehole, well, spring or watercourse. If microbiological contamination is a risk on your supply — and on most private sources it is — the disinfection stage has to be something that can be monitored, typically ultraviolet irradiation or chlorination, and reverse osmosis sits alongside it rather than instead of it. Treatment design for a private supply belongs to a risk assessment carried out with the local authority, and the wider water treatment guide on this site sets out how those stages fit together.

There is a second, smaller hygiene point that applies to mains installations too. An RO unit holds treated water in a storage vessel between uses, and treated water with almost nothing left in it is not self-protecting. Manufacturers specify sanitising and membrane replacement intervals for that reason, and a unit that has been ignored for years is not doing what its owner believes it is doing.

Two figures matter and they move independently. The installation is driven by where the unit will sit and what has to be created around it — a dedicated tap and a hole in the worktop or sink, a drain connection for the reject flow, isolation valves, whether a booster pump is needed to meet the unit's pressure requirement, whether remineralisation is being included, and the notification to the water undertaker. The running cost is driven by how many stages the unit has, what each consumable costs and how often the manufacturer wants it changed, plus the extra water going to drain on a metered supply. A cheap unit with expensive proprietary cartridges is a false economy that only shows up in year two.

The role LokalMatch plays is introducing you to the people who quote. Explain once what you want the system to do and whether you are on mains or a private supply, add your postcode, and water treatment installers in your area make contact with you. Homeowners are never charged; the pros pay for the requests that reach them. LokalMatch does not sell, fit or service reverse osmosis equipment, has nothing to do with pricing, and does not vet, rank or recommend anyone who gets in touch, so asking about consumable costs, remineralisation and who notifies your water company is down to you.