Which Should You Choose? Complete UK Comparison Guide 2026
It's the most common question I get asked: "Should I get a reverse osmosis system or is a carbon filter good enough?"
After 24 years in water filtration, here's my honest answer: it depends on what you're trying to remove. Both filter types have their place, and choosing the wrong one means either wasting money on overkill or not actually solving your water problem.
In this guide, I'll break down exactly what each filter type does (and doesn't do), the real costs involved, and help you make the right choice for your specific situation.
Adsorption-based filtration
Carbon filters work through adsorption—contaminants stick to the surface of activated carbon as water passes through. Think of it like a sponge that attracts and holds certain chemicals.
Membrane-based filtration
RO forces water through a semi-permeable membrane with pores so small (0.0001 microns) that virtually nothing except water molecules can pass through. It's like a molecular sieve.
| Feature | Carbon Filter | Reverse Osmosis |
|---|---|---|
| Upfront Cost | £50-150 | £200-600 |
| Annual Filter Cost | £30-60 | £50-100 |
| Water Waste | None | 1:1 to 5:1 ratio |
| Installation | Easy (DIY) | Moderate (under-sink) |
| Chlorine Removal | ||
| Taste Improvement | ||
| Lead Removal | Some models* | |
| PFAS Removal | Partial (50-70%) | |
| Heavy Metals | ||
| Fluoride Removal | ||
| Limescale/TDS | ||
| Bacteria/Viruses | ||
| Renter-Friendly | Some models |
*Only NSF 53 certified carbon filters can reduce lead
Chlorine & Chloramine
95-99% removal
Bad Taste & Odours
Excellent improvement
Some Organic Chemicals
Pesticides, herbicides, VOCs
Some PFAS
50-70% (varies by type)
Everything Carbon Removes
Plus much more...
Heavy Metals
Lead, arsenic, mercury (99%+)
PFAS/Forever Chemicals
95-99% removal
Dissolved Minerals (TDS)
Hardness, limescale prevention
Fluoride & Nitrates
85-95% removal
Bacteria & Viruses
99.99% removal
Note: RO also removes beneficial minerals. Some systems include remineralisation stages to add them back.
| Cost Element | Carbon Filter | RO System |
|---|---|---|
| Initial Purchase | £80 | £400 |
| Installation | £0 (DIY) | £0-100 |
| Filters (5 years) | £200 | £350 |
| Water Waste Cost | £0 | £50-100* |
| Electricity | £0 | £10-20 |
| 5-Year Total | £280 | £810-970 |
*Modern efficient RO systems (1:1 ratio) have much lower water waste costs
Under-sink carbon block filter with excellent chlorine and taste improvement. NSF 42 certified. Great value at around £80 with £40/year filter costs.
Note: Not suitable for lead or heavy metal concerns. For those issues, choose an RO system.
Tankless RO with 1:1 waste ratio (industry-leading efficiency). Removes 99%+ of contaminants including lead, PFAS, and heavy metals. Around £400 with £70/year filters.
Reverse osmosis removes more contaminants (including dissolved solids, heavy metals, and PFAS) but costs more and wastes water. Carbon filters are better for taste improvement and chlorine removal at a lower cost. The 'better' choice depends on your specific water concerns—RO for comprehensive purification, carbon for taste and basic filtration.
Most UK households don't need reverse osmosis since mains water meets safety standards. However, RO is recommended if you have lead pipes, want to remove PFAS/forever chemicals, have very hard water, or want the purest possible drinking water. For basic taste improvement and chlorine removal, a quality carbon filter is usually sufficient.
Reverse osmosis removes: dissolved minerals (TDS), heavy metals (lead, arsenic, mercury), fluoride, nitrates, sodium, and most PFAS. Carbon filters cannot remove these dissolved substances—they primarily remove chlorine, chloramine, some organic chemicals, and improve taste and odour. RO removes up to 99% of contaminants; carbon typically removes 50-95% of what it targets.
Traditional RO systems waste 3-5 litres for every 1 litre of filtered water (3:1 to 5:1 ratio). Modern tankless systems like the Waterdrop G3P600 have improved to 1:1 or 2:1 ratios. Carbon filters waste no water. For a family of four, traditional RO might add £15-20/year to water bills; modern efficient systems add much less.
Carbon filters are significantly cheaper. A quality carbon filter costs £50-150 upfront with £30-60/year in replacement filters. Reverse osmosis systems cost £200-600 upfront with £50-100/year in filters, plus additional water waste costs. Over 5 years, carbon costs around £200-400 total; RO costs £450-1,000+.
Only specially designed carbon filters with NSF 53 certification for lead reduction can remove lead—and even then, effectiveness varies (typically 93-99%). Standard carbon filters do NOT remove lead. If lead is your concern, reverse osmosis (99%+ removal) or a certified lead-reduction carbon filter is essential. Always check for NSF 53 certification.
Use our filter finder tool to get a personalised recommendation based on your specific water concerns, budget, and installation situation.
Water Filtration Specialist | 24+ Years Experience
Keith has installed hundreds of both carbon and RO systems across the UK. His recommendations are based on real-world performance, not just manufacturer claims.
Read full bioThis comparison is based on typical products in each category. Individual filter performance varies by model and certification. Always check NSF certifications for specific contaminant removal claims. Last updated: January 2026.