Water filters work by passing water through one or more media that trap or chemically attract contaminants. The most common is activated carbon, which adsorbs chlorine, odours and many chemicals, while other methods include ion exchange (for metals and hardness), reverse osmosis membranes (for dissolved solids) and UV light (for bacteria). Different filters use different methods, which is why they remove different things. This guide explains how water filters work in plain terms.
Water filters pass water through media that trap or attract contaminants. Activated carbon adsorbs chlorine and chemicals; ion exchange swaps out metals and hardness; reverse osmosis membranes block dissolved solids; UV kills bacteria. Different methods remove different things.
The Main Filtration Methods
| Method | How it works | Targets |
|---|---|---|
| Activated carbon | Adsorbs contaminants onto its surface | Chlorine, odours, many chemicals |
| Ion exchange | Swaps ions (e.g. lead for harmless ones) | Lead, some metals, hardness |
| Reverse osmosis | Forces water through a fine membrane | Dissolved solids, lead, fluoride |
| Sediment filter | Physically strains particles | Sand, grit, rust |
| UV light | Disrupts microorganism DNA | Bacteria, viruses |
Key Takeaway: No single method does everything. Carbon handles taste and chemicals, ion exchange handles metals, reverse osmosis handles dissolved solids, and UV handles microbes, which is why thorough systems stack several methods together.
Activated Carbon
Activated carbon has a huge surface area that adsorbs (binds) chlorine, odours and many chemicals as water passes through. It is the most common method in pitchers, faucet and under-sink filters. See what water filters remove.
Ion Exchange
Ion exchange resins swap unwanted ions like lead and hardness minerals for harmless ones, often paired with carbon in better pitchers.
Reverse Osmosis
Reverse osmosis forces water through a very fine membrane that blocks dissolved solids, lead, fluoride and more, the most thorough common method. See what is reverse osmosis.
Sediment and UV
Sediment filters strain out particles like sand and rust; UV light disrupts the DNA of bacteria and viruses without chemicals. See do water filters remove bacteria.
FAQ
How do water filters work?
They pass water through media that trap or attract contaminants. Carbon adsorbs chlorine and chemicals, ion exchange swaps metals, reverse osmosis blocks dissolved solids, and UV kills bacteria.
What is the most common type of water filter?
Activated carbon, used in most pitchers, faucet and under-sink filters, which adsorbs chlorine, odours and many chemicals.
Do all water filters remove the same things?
No. Different methods remove different contaminants, which is why you should check what each filter is certified to reduce.
Bottom Line
Water filters work by passing water through media, carbon, ion exchange, reverse osmosis, sediment or UV, that trap or attract contaminants, and different methods remove different things. Check what each filter targets. See our what water filters remove and how to choose a water filter guides.
