What is a reverse osmosis water filter?

A reverse osmosis water filter forces tap water through a semi-permeable membrane whose pores reject dissolved contaminants, backed by carbon pre- and post-filters. It removes the widest range of anything available for home use, including PFAS, fluoride, nitrates, heavy metals, and hardness minerals.

How much does a reverse osmosis system cost in the UK?

The systems we review run from £450 to £650 up front. Budget roughly £100-£150 a year for replacement filters depending on the model, counting a share of the main RO filter, which lasts about two years. Tankless designs cost more up front but save cupboard space and waste less water.

Is reverse osmosis water safe to drink?

Yes. RO water is safe and is used worldwide for drinking water. The debate is about minerals: RO strips calcium and magnesium along with the contaminants. A balanced diet supplies far more of both than tap water does, and several systems add a remineralisation stage for taste.

Does reverse osmosis waste a lot of water?

Less than older systems did. Modern tankless RO systems like the Waterdrop G3P600 and Frizzlife PD600 run at 2:1, meaning about 1 litre goes down the drain for every 2 litres you drink. Older systems can waste 4 litres for every 1 you drink.

Does reverse osmosis remove minerals I need?

RO removes most dissolved minerals. Some systems add minerals back with a remineralisation stage. For most people, a balanced diet provides enough minerals without relying on tap water.

Reverse Osmosis Systems

The gold standard. RO systems push water through a semi-permeable membrane, removing virtually everything.

Best for: Households with PFAS, fluoride, or nitrate concerns · £450–£650

Read our full guide: Best Reverse Osmosis System UK

A reverse osmosis water filter pushes mains water through a semi-permeable membrane with pores small enough to reject dissolved contaminants that carbon filters let through: PFAS, fluoride, nitrates, heavy metals, and the hardness minerals behind limescale. A carbon pre-filter protects the membrane from chlorine, and a post-filter polishes the taste on the way out.

In the UK the case for an RO system is specific rather than general. Tap water here meets strict legal standards, but PFAS currently has no statutory limit in England and Wales, fluoride passes every other filter type, and most of the country lives with hard water. Reverse osmosis is the one home technology that answers all three at once, which is why it anchors the top of our removal comparison.

The practical trade-offs: RO wastes some water (modern tankless systems send about 1 litre down the drain for every 2 you drink), strips beneficial minerals along with the bad (remineralisation stages exist for that), and filters drinking water at one tap rather than the whole house. Check your postcode below to see whether your water actually carries the contaminants an RO system is built for.

Not sure which to pick? Check your water first.

Waterdrop G3P600 Reverse Osmosis

Reverse Osmosis · NSF/ANSI 58, NSF/ANSI 372

Why it fits: Removes 12+ contaminants including PFAS and fluoride
Tankless design saves under-sink space
Smart TDS monitoring panel shows real-time water quality
Trade-offs: Professional installation recommended — plumbing required
Higher upfront cost than any jug or tap filter

Typical price

£550approx.

Check current price at Waterdrop

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Frizzlife PD600 Under Sink RO

Reverse Osmosis · NSF/ANSI 58

Why it fits: Lower price than Waterdrop G3P600 with similar performance
Puts minerals back after filtering, so the water tastes less flat
Screen shows how clean the water is and when a filter is due
Trade-offs: Slightly noisier pump than Waterdrop
Fewer certifications — NSF 58 only

Typical price

£450approx.

Check current price at Frizzlife

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Osmio Zero 2.0 Countertop RO

Reverse Osmosis

Why it fits: Plugs into a socket — the only RO here that needs no plumbing, so renters can use it
Wastes 1 litre for every 5 produced, far less than a typical under-sink RO
Dispenses at drinking temperature through to near-boiling, so it replaces the kettle too
Trade-offs: No NSF or WRAS certification stated
Osmio does not publish a filter replacement interval, so annual running cost is unclear

Typical price

£495approx.

Check current price at Osmio

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Osmio Fusion 2.0 Installed RO

Reverse Osmosis

Why it fits: Bioceramic remineralisation stage puts minerals back and lifts pH, which flat RO water lacks
Widest contaminant list here, covering fluoride and nitrates as well as chlorine and lead
UK company with UK-based support and spares
Trade-offs: No NSF or WRAS certification stated, unlike the Waterdrop G3P600
Filters need replacing every 6 months at around £126/year

Typical price

£495approx.

Check current price at Osmio

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Osmio Fusion 3.0 Installed Hydrogen RO

Reverse Osmosis

Why it fits: Direct feed without a storage tank, so there is no waiting for the tank to refill
Adds a hydrogen generator and chilled water in the same unit
Same broad contaminant coverage as the Fusion 2.0
Trade-offs: £155 more than the Fusion 2.0 for features unrelated to filtration quality
Manufacturer warranty is only 12 months, shorter than most systems here

Typical price

£650approx.

Check current price at Osmio

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Side-by-side comparison

Filter	Price	Rating	Annual Cost
Waterdrop G3P600 Reverse Osmosis (opens in new tab) Maximum contaminant removal including PFAS and fluoride	£550	4.6	£144/yr
Frizzlife PD600 Under Sink RO (opens in new tab) Best value reverse osmosis for UK kitchens	£450	4.5	£107/yr
Osmio Zero 2.0 Countertop RO (opens in new tab) Renters and anyone who wants RO water without a plumber	£495	4.4	£130/yr
Osmio Fusion 2.0 Installed RO (opens in new tab) Households wanting remineralised RO water from a UK supplier	£495	4.3	£126/yr
Osmio Fusion 3.0 Installed Hydrogen RO (opens in new tab) Buyers who specifically want tankless RO with hydrogen and chilled water	£650	4.1	—

Common questions

What is a reverse osmosis water filter?: A reverse osmosis water filter forces tap water through a semi-permeable membrane whose pores reject dissolved contaminants, backed by carbon pre- and post-filters. It removes the widest range of anything available for home use, including PFAS, fluoride, nitrates, heavy metals, and hardness minerals.
How much does a reverse osmosis system cost in the UK?: The systems we review run from £450 to £650 up front. Budget roughly £100-£150 a year for replacement filters depending on the model, counting a share of the main RO filter, which lasts about two years. Tankless designs cost more up front but save cupboard space and waste less water.
Is reverse osmosis water safe to drink?: Yes. RO water is safe and is used worldwide for drinking water. The debate is about minerals: RO strips calcium and magnesium along with the contaminants. A balanced diet supplies far more of both than tap water does, and several systems add a remineralisation stage for taste.
Does reverse osmosis waste a lot of water?: Less than older systems did. Modern tankless RO systems like the Waterdrop G3P600 and Frizzlife PD600 run at 2:1, meaning about 1 litre goes down the drain for every 2 litres you drink. Older systems can waste 4 litres for every 1 you drink.
Does reverse osmosis remove minerals I need?: RO removes most dissolved minerals. Some systems add minerals back with a remineralisation stage. For most people, a balanced diet provides enough minerals without relying on tap water.

We may earn a commission when you buy through our links, at no extra cost to you. Recommendations are based on water quality data, not sponsorship. Affiliate disclosure