This is the most important decision in home water filtration, and it’s often misunderstood. Reverse osmosis (RO) and activated carbon filter water in fundamentally different ways and remove different things. Buy the wrong type and you’ll either overspend or under-filter. Here’s how to choose for a UK home.
The core difference
- Carbon filters (including most jugs and many simple under-sink cartridges) work by adsorption — contaminants stick to the carbon. Great for chlorine, taste and odour; limited against dissolved minerals and many contaminants.
- Reverse osmosis pushes water through a semi-permeable membrane that physically blocks the vast majority of dissolved contaminants — TDS, PFAS, lead, fluoride and more. It’s far more thorough, and the only common home method certified against that full range.
In short: carbon improves water; reverse osmosis purifies it.
What each removes
| Carbon filter | Reverse osmosis | |
|---|---|---|
| Chlorine, taste & odour | Yes | Yes |
| TDS / dissolved minerals | No | Yes |
| Limescale hardness | No | Yes |
| Lead & heavy metals | Some (if certified) | Yes (certified) |
| PFAS | Variable / limited | Yes (certified models) |
| Fluoride | No | Yes |
| Microplastics | Some | Yes |
Cost and water taste
- Carbon is cheaper upfront (a jug is £20–£40; a plumbed carbon cartridge more) and adds nothing to your water. But cartridges need frequent changes and do little for hard water.
- Reverse osmosis costs more (£375–£700) and removes beneficial minerals along with the bad — some people find pure RO water tastes “flat” and add a remineralisation stage. It’s the only option that genuinely tackles UK hard water and the contaminants of growing concern.
Which should a UK home buy?
It comes down to what’s actually in your water and what bothers you:
- You only want better-tasting water and you’re on soft water → a carbon filter (even a good jug) is enough. Don’t overspend on RO.
- You’re in a hard-water area (London, the South East, the Midlands) → reverse osmosis. Only RO meaningfully reduces the dissolved minerals behind limescale. See best water filter for hard water.
- You’re worried about PFAS, lead or fluoride → reverse osmosis with the right certifications. Carbon is too variable. See our PFAS water filter guide.
- You’re a renter → a countertop RO unit like the AquaTru Classic gives you RO-grade filtration with no plumbing.
The verdict
If your only goal is taste on soft water, a carbon filter is the sensible, cheap choice. For hard water, PFAS, lead or fluoride — which covers most of the reasons UK households filter — reverse osmosis is worth the extra. The good news: modern RO systems like the Waterdrop G3P600 include excellent carbon stages too, so you get the best of both.
Frequently asked questions
What's the difference between reverse osmosis and a carbon filter?
Carbon filters adsorb contaminants like chlorine and improve taste, but do little for dissolved minerals. Reverse osmosis forces water through a membrane that blocks the vast majority of dissolved contaminants including TDS, PFAS, lead and fluoride. RO is far more thorough.
Do I need reverse osmosis or is a carbon filter enough?
If you only want better-tasting water on soft water, a carbon filter is enough. If you have hard water, or worry about PFAS, lead or fluoride, you need reverse osmosis — carbon can't reliably remove those.
Does a carbon filter remove PFAS?
Only variably. Some high-quality carbon filters reduce some PFAS, but performance differs widely and drops as the filter ages. For reliable, certified PFAS reduction, choose a reverse osmosis system certified to NSF/ANSI P473 or 53/58.
Does reverse osmosis remove limescale?
Yes. RO reduces the dissolved calcium and magnesium that cause limescale, which is why it's the right choice for hard-water UK areas. A carbon filter does not meaningfully reduce hardness.