Five filtration technologies, how each one works, what it removes — and which type makes sense for your situation.
Each technology uses a different physical or chemical process to remove contaminants
Activated carbon has an enormous surface area (1 gram can have the surface area of a football pitch). Contaminant molecules adsorb — chemically bond to — the carbon surface as water passes through. Carbon block filters are denser and more effective than granular activated carbon (GAC), especially for organic compounds and some disinfection byproducts.
Water is forced under pressure through a semi-permeable membrane with pores approximately 0.0001 microns — small enough to block dissolved salts, metals, and most organic molecules. Modern under-sink RO systems use 4–7 stages: sediment pre-filter, carbon pre-filter, RO membrane, carbon post-filter, and sometimes remineralisation or UV stages. Tankless RO systems (like Waterdrop G3P800) deliver filtered water on demand without a storage tank.
A UV-C lamp (typically 254nm wavelength) irradiates water as it flows through a chamber. UV light damages the DNA of bacteria, viruses, and protozoa, preventing them from reproducing. UV is effective against chlorine-resistant pathogens like Cryptosporidium and Giardia. It is always paired with mechanical filtration, as suspended particles can shield microorganisms from UV exposure.
Ceramic filters use a porous clay matrix with pore sizes of 0.2–0.5 microns. Hollow-fibre ultrafiltration uses bundles of hollow polymer fibres with similar pore sizes. Water passes through; anything larger than the pore size (bacteria, cysts, sediment) is mechanically blocked. Many ceramic filters also incorporate silver to prevent bacterial growth within the filter medium. Ceramic filters can be cleaned and reused multiple times.
Ion exchange resins carry a charge that attracts specific ions from water and releases a different ion in exchange. Salt-based water softeners swap calcium and magnesium ions (hardness) for sodium ions. Specialised resins can target heavy metals, nitrates, or arsenic. KDF (kinetic degradation fluxion) media uses a redox process to remove chlorine and heavy metals. Ion exchange resins require periodic regeneration (salt for softeners, acid/base for others).
Which technology removes which contaminant
| Contaminant | Activated Carbon | Reverse Osmosis | UV | Ceramic | Ion Exchange |
|---|---|---|---|---|---|
| Chlorine / Taste | ✓ | ✓ | ✗ | ✗ | ✗ |
| Lead / Heavy Metals | ✗ | ✓ | ✗ | ✗ | Partial |
| PFAS (Forever Chemicals) | Partial | ✓ | ✗ | ✗ | ✗ |
| Nitrates | ✗ | ✓ | ✗ | ✗ | ✓ |
| Bacteria | ✗ | ✓ | ✓ | ✓ | ✗ |
| Viruses | ✗ | ✓ | ✓ | ✗ | ✗ |
| Microplastics | ✗ | ✓ | ✗ | ✓ | ✗ |
| Water Hardness | ✗ | ✓ | ✗ | ✗ | ✓ |
A pitcher filter or under-sink carbon block is sufficient. Affordable, easy to maintain. Best entry point.
Reverse osmosis is the only reliable solution for heavy metal removal. Under-sink RO makes sense long-term.
RO or specialist PFAS-rated carbon block. Standard pitcher filters are insufficient for PFAS removal.
UV + ceramic combination addresses biological risk. Add carbon stage for chemical protection.
RO removes hardness without adding sodium. Ion exchange softeners also work but require salt maintenance.
Multi-stage RO system (sediment + carbon + membrane + remineralisation) covers all major risk categories.
Read more → Health Effects of Tap Water Contaminants ↗
Our reviews explain exactly what each filter removes — with independent test data and real-world scores.
See Top 5 Filters →Positive stories about rivers, restoration, and clean water across the Mediterranean and beyond.
The Council of the EU officially adopted the European Water Resilience Strategy, committing to restore rivers, lakes, and wetlands and guaranteeing clean, affordable water for all Europeans by addressing pollution at the source.
wareg.org ↗Eight obsolete river barriers were removed at Plitvice Lakes National Park — the first dam removals in Croatia's history — reconnecting 7.6 km of river and restoring habitat for the endangered Danube trout.
damremoval.eu ↗A 30-metre dam on the Liri River was dismantled by Rewilding Apennines, freeing over 11 km of waterway. Thousands of juvenile Mediterranean trout were released to repopulate the restored river.
rewildingeurope.com ↗MedINA published Greece's first practical roadmap for removing river barriers — a critical step that unlocks funding and policy support for dam removal across the Mediterranean region.
med-ina.org ↗Authorities in Spain's Basque Country began breaking down a 43-metre-high dam on the Leitzaran River — one of the largest obsolete dams in Europe — letting the river flow freely for the first time in decades. The EU-backed LIFE Kantauribai project will reconnect fish habitats and restore the ecosystem.
euroweeklynews.com ↗A landmark report found 23 countries removed river barriers in 2024 — up 11% year-on-year. Spain dismantled 96 dams, France 128, Finland 138, bringing the EU closer to its goal of 25,000km of free-flowing rivers by 2030.
theguardian.com ↗The European Commission adopted the European Water Resilience Strategy in June 2025, with the European Investment Bank pledging €15 billion (2025–2027) for water restoration. The strategy sets a path to clean, affordable water for all Europeans by 2050.
environment.ec.europa.eu ↗