Reverse Osmosis Water Filters UK: Are They Worth It?

What is a reverse osmosis water filter?

Reverse osmosis (RO) uses water pressure, sometimes boosted by a pump, to push water through a semi-permeable membrane with extremely small pores. Water molecules pass; most dissolved salts, metals and larger molecules are held back and flushed to a drain. A typical home system has three to five stages: a sediment pre-filter, a carbon pre-filter (to protect the membrane from chlorine), the RO membrane, then a carbon "polishing" filter and sometimes a remineralising stage.

Because it removes dissolved substances that carbon cannot, RO is the broadest type of home filter. In the Duke and NC State study of filters in real homes, under-sink RO systems removed nearly all of the PFAS ("forever chemicals") tested (Herkert et al. 2020).

Are reverse osmosis water filters worth it in the UK?

It depends on why you want one. UK tap water already meets tight legal standards (Which?). RO makes most sense if:

• your home predates 1970 and may have lead pipes (DWI), and you want a certified backstop while pipes are replaced;
• you want to lower PFAS exposure further than the DWI's precautionary 0.1 micrograms per litre guideline for 48 PFAS (DWI);
• you are on a private supply, or want lower nitrate, fluoride or dissolved solids.

If you mainly want better taste, a carbon jug or under-sink filter is cheaper and wastes no water.

Our picks at a glance

How we chose

We prioritised RO systems with a public NSF/ANSI 58 listing for the exact model. NSF/ANSI 58 is the standard for home RO: it tests TDS (total dissolved solids) reduction and named health claims such as lead, arsenic, fluoride and nitrate. PFOA/PFOS claims sit under NSF/ANSI 53 or 58, and NSF says a PFAS claim requires reduction to below 20 parts per trillion (NSF). Listings can come from NSF, IAPMO R&T or WQA. We verified UK prices and noted waste ratio, power, installation and hardness limits.

What should you check before buying an RO system?

Waste water ratio

All RO systems send some water to drain to carry away what the membrane rejects. Modern tankless units quote a "pure-to-drain" ratio of 2:1 or 3:1, meaning 1 litre to drain for every 2 or 3 litres you drink. AquaTru says about 3 litres of tap water make 1 litre of filtered water. The waste is ordinary tap water with more minerals; some people use it for cleaning or plants.

Remineralisation

RO removes most calcium and magnesium, which can make water taste flat. The WHO has reviewed the health considerations of long-term drinking of demineralised water and how it can be reconstituted (WHO). Most of your minerals come from food, but a remineralising post-filter improves taste and is a reasonable extra. Treat "alkaline" marketing as a taste preference, not a health benefit.

Hard water

England has some of the hardest water in Europe. Hardness can scale an RO membrane and shorten its life. AquaTru's stated limit is 10 grains per gallon (about 171 mg/L as calcium carbonate); above that it advises softening the feed. Check your water company's hardness figure before buying.

Countertop or under-sink?

Under-sink RO needs a plumber, a drain connection, usually a socket, and a separate tap, but is hidden and plumbed in. Countertop RO plugs in and you fill it by hand, which suits renters but takes worktop space and the waste tank needs emptying.

Can you fit reverse osmosis yourself?

Countertop units need no fitting at all. Under-sink systems involve tapping into the cold supply, drilling for a tap and connecting a drain saddle to the waste pipe. Confident DIYers manage it, but a mistake can mean leaks in a cupboard you rarely look in. A WaterSafe-accredited plumber, as the DWI suggests for work on drinking water pipes (DWI), is the lower-risk route and lets you add a leak detector at the same time.

Our picks in detail

Waterdrop G3P600 Reverse Osmosis System: best under-sink RO

IAPMO R&T certifies the G3P600 to NSF/ANSI 58 (including lead and TDS), 53 (including PFOA and PFOS) and 42 (TapWaterData). It is tankless, fills a glass quickly and sends only 1 litre to drain for every 2 filtered. Caveat: it needs a plumber, power and a dedicated tap, and remineralisation is a separate cartridge.

AquaTru Under Sink Reverse Osmosis System: most certified claims

The ATU200 is IAPMO-listed under NSF/ANSI 42, 53, 58 and 401, adding microplastics and some medicines to lead and PFOA/PFOS (TapWaterData). At £375 it is slightly cheaper than the Waterdrop. Caveat: about 3:1 tap-to-filtered water and a 10 grains per gallon hardness limit, which many English homes exceed.

AquaTru Classic Countertop Reverse Osmosis: best countertop

The most thoroughly certified countertop RO we found: IAPMO lists it under NSF/ANSI 42, 53, 58 and 401 (TapWaterData). No plumbing needed. Caveat: £475, bulky, and sold out on AquaTru UK when we checked.

Waterdrop M6SL Mineral Countertop Reverse Osmosis: best value countertop

A plug-in unit with a 3:1 ratio that adds minerals back for taste, at £269. Waterdrop states NSF/ANSI 58 and 372 certification. Caveat: Waterdrop does not name the certifier or which claims are covered, and we found no public listing, so we grade it moderate.

Sküma MY™ Station Countertop Reverse Osmosis: also consider

A compact countertop RO from a UK brand with swappable mineral profiles, popular with coffee lovers. Sküma claims reduction of 20 PFAS and validation by an independent French lab. Caveat: no certifier, certification or lab is named and no waste ratio is published, so the evidence is limited.

AquaTru Carafe Countertop Reverse Osmosis: also consider

IAPMO lists the AT100 model in this family under NSF/ANSI 42, 53, 58 and 401, and filtered water goes into a glass carafe (TapWaterData). Caveat: sold out on AquaTru UK when checked.

What the evidence says

• RO is the broadest home option. Under-sink RO and two-stage systems removed nearly all PFAS in real homes, unlike most jugs (Herkert et al. 2020).
• Certification is per claim. Look for NSF/ANSI 58 plus the specific contaminant you care about (NSF).
• Even good RO is not 100%. Belgian consumer group Test-Achats notes RO removes nearly all PFAS but also strips minerals, wastes water and costs more (Test-Achats).
• Maintenance matters. Pre-filters protect the membrane; skipping changes shortens its life and can lower performance.

What to avoid

• "RO" units with no NSF/ANSI 58 listing for the exact model.
• Old-style tank systems with no stated ratio; some waste several litres per litre.
• Fitting RO to softened water without checking the sodium; the DWI advises an unsoftened drinking tap (DWI).
• Paying extra for "alkaline" or "hydrogen" claims; these are taste features.

Bottom line

A certified RO system is the most thorough way to lower lead, PFAS and dissolved solids at home. If you own your home, the Waterdrop G3P600 balances certification, speed and low waste; the AquaTru Under Sink covers more listed claims. If you rent, the AquaTru Classic is the best-certified countertop when in stock, with the Waterdrop M6SL as a cheaper option. If you only want better taste, skip RO and see our best water filter guide.