KDF vs. Carbon Water Filters: What's the Difference?
Shop for a water filter and you'll see two terms again and again: carbon (often listed as GAC, for granular activated carbon) and KDF. They work in completely different ways, and the best filters use both. Here's what each one does and how to choose.
What is a carbon (GAC) filter?
Activated carbon is carbon that has been processed to be extremely porous, giving it a huge surface area. As water flows through, chlorine and many organic chemicals stick to that surface. This process is called adsorption. Carbon is excellent at improving the taste and smell of water, which is why it's in almost every drinking water filter.
Carbon has two weak spots. Bacteria can grow on the trapped material over time, and carbon is less effective in hot water.
What is KDF?
KDF stands for kinetic degradation fluxion. It's a filter media made of high-purity copper and zinc granules. Instead of trapping chlorine, KDF removes it through a chemical reaction (called redox) that changes free chlorine into harmless chloride. KDF media is also used to help reduce some dissolved heavy metals.
KDF has two big strengths: it holds up well in hot water, and it discourages the growth of bacteria, algae and fungi inside the filter. For a deeper look, read What is kinetic degradation fluxion (KDF) media?
KDF vs. carbon at a glance
| Carbon (GAC) | KDF | |
| How it works | Adsorption (contaminants stick to the carbon) | Chemical reaction (redox) |
| Chlorine | Reduces | Reduces |
| Taste and odor | Excellent | Good |
| Hot water | Less effective | Works well |
| Bacteria growth in the filter | Can be a problem | Discourages growth |
| Best for | Drinking water | Showers and pairing with carbon |
Why the best filters use both
Combining KDF and carbon gives you the strengths of each. The KDF stage reduces chlorine and keeps the filter bacteriostatic (resistant to bacteria growth), and the carbon stage polishes the taste and smell of the water. That's why every USA Filtration drinking water filter uses bacteriostatic GAC/KDF media, which prevents bacteria growth inside the filter for up to 36 months.
Which should you choose?
- For your shower: choose KDF, because it works well in hot water. Try the USA-75 KDF Shower Head Water Filter.
- For drinking water: choose a GAC/KDF combination, like the USA-100 under sink filter or the USA-50 countertop filter.
- For your whole home: choose a whole house system like the USA-300.
Not sure which filter is right for you? Contact us or call 888-672-3458.