Activated Carbon Filters: How They Work & What They Remove (2026 Guide)

Activated carbon filters — also known as charcoal water filters or carbon water filters — are one of the most effective and affordable ways to improve your drinking water. Whether you call them carbon filters, charcoal filters, or activated charcoal filters, they all work the same way: trapping contaminants as water passes through millions of tiny pores.

This comprehensive guide explains exactly how activated carbon filters work, what they remove (and what they don't), and how to choose between the two main types for your home.

What Is Activated Carbon?

Activated carbon is a specially processed form of carbon with an incredibly porous structure. Typically made from coconut shells, bamboo, or wood, the raw material is heated to extremely high temperatures in a process called "activation." This creates a vast network of microscopic pores that can trap contaminants through a process called adsorption.

To put this into perspective: one gram of activated carbon has a surface area of over 3,000 square metres — nearly half a football pitch. This enormous surface area is what makes activated carbon so effective at water purification.

Activated Carbon vs Charcoal Filters: Is There a Difference?

You'll often see water filters marketed as "activated carbon filters," "charcoal filters," or "activated charcoal filters." The good news? These terms all mean the same thing.

The only difference is marketing terminology: "activated carbon" is the technical term used in the water treatment industry, while "charcoal filter" is the common consumer term. When shopping for water filters in the UK, you can use these terms interchangeably.

How Do Activated Carbon Filters Work?

Activated carbon purifies water through two mechanisms:

1. Physical Adsorption: As water passes through the filter, contaminant molecules are drawn into the millions of tiny pores on the carbon's surface and become trapped. The carbon acts like a sponge, holding onto these impurities while clean water flows through.

2. Chemical Reaction: When chlorine comes into contact with activated carbon, a chemical reaction converts it into harmless chloride ions. This is why carbon filters are so effective at removing the chlorine taste and smell from tap water.

Several factors affect filtration performance: water flow rate (slower = better filtration), water temperature, pH levels, and contact time with the carbon media.

GAC vs Carbon Block Filters: Which Should You Choose?

The two most common types of activated carbon filters for home use are Granular Activated Carbon (GAC) and Carbon Block filters. Here's how they compare:

Our recommendation: Choose GAC filters when you need higher flow rates and are primarily filtering for taste and odour improvement. Choose carbon block filters when you need maximum contaminant removal and finer filtration. Many systems use both types together for comprehensive treatment.

What Do Activated Carbon Filters Remove?

According to research by the US Environmental Protection Agency, activated carbon is the only filter material that removes all 32 identified organic contaminants, all 12 herbicides, and all 14 pesticides commonly found in drinking water.

Key Contaminants Removed

Chlorine: The most noticeable improvement for most users. High-quality activated carbon filters remove up to 95% of free chlorine, eliminating the chemical taste and smell from tap water.

Chlorine By-products (THMs): Trihalomethanes are potentially carcinogenic compounds created when chlorine reacts with organic matter. Activated carbon excels at removing these — it's more effective than any other filtration technology for THM removal.

Pesticides and Herbicides: Including glyphosate (Roundup), atrazine, and other agricultural chemicals that can enter water supplies through groundwater contamination.

PFAS/PFOS: These "forever chemicals" from non-stick coatings, firefighting foam, and industrial processes are a growing concern. Activated carbon has been shown to effectively remove PFAS compounds including PFOA and PFNA.

Pharmaceuticals: Medication residues that enter water supplies through improper disposal or incomplete treatment at water facilities. Quality carbon block filters can remove up to 95% of pharmaceutical traces.

Microplastics: Carbon block filters with a 5-micron rating or smaller, such as the Omnipure Q5586, can remove microplastic particles larger than 5 microns.

What Activated Carbon Filters Cannot Remove

Dissolved Minerals (Hardness): Calcium, magnesium, and other minerals that cause limescale pass straight through carbon filters. If you have hard water, you'll need a water softener or reverse osmosis system.

Bacteria and Viruses: Standard carbon filters don't remove microorganisms. If you're on a private water supply (borehole, well, or spring), you'll need UV sterilisation or ultrafiltration in addition to carbon filtration.

Fluoride: Activated carbon does not effectively remove fluoride. You'll need a reverse osmosis system or specialised media (activated alumina or bone char) for fluoride reduction.

Heavy Metals: Standard carbon has limited effectiveness against lead, mercury, and arsenic. Look for filters with KDF media or choose a reverse osmosis system for heavy metal removal.

Total Dissolved Solids (TDS): Carbon doesn't significantly reduce TDS readings. If lowering TDS is important to you, reverse osmosis is the appropriate technology.

The solution? For comprehensive water purification, activated carbon works best as part of a multi-stage filtration system. Many under-sink and whole house systems combine carbon with other technologies for complete protection.

How to Choose the Right Carbon Filter

Consider these factors when selecting an activated carbon filter:

1. Your Water Quality Concerns: If you mainly want to improve taste and remove chlorine, a basic GAC filter will suffice. For broader contaminant removal, choose a carbon block filter or multi-stage system.

2. Flow Rate Requirements: Whole house applications need higher flow rates (GAC filters). Point-of-use drinking water filters can use slower-flow carbon blocks for better filtration.

3. Certification: Always look for filters with third-party certifications from organisations such as NSF or WRAS, which verify the filter meets specific contaminant reduction claims.

4. Replacement Schedule: Most carbon filters should be changed every 6 months or when they reach their rated capacity — whichever comes first. This prevents bacterial growth and ensures continued effectiveness.

Conclusion

Activated carbon filters remain the most popular and cost-effective water filtration technology for good reason. They excel at removing chlorine, organic chemicals, pesticides, and the compounds that affect your water's taste and odour.

Understanding the difference between GAC and carbon block filters — and knowing what carbon can and cannot remove — helps you make the right choice for your household. For most UK homes on mains water, a quality activated carbon filter will significantly improve your water quality at an affordable price.

Browse our full range of activated carbon filters or contact our team for personalised recommendations.

Frequently Asked Questions

Are carbon water filters safe?

Yes, carbon water filters are completely safe and will only improve your water quality. Always look for third-party certifications from organisations such as NSF or WRAS, and replace your filter according to manufacturer recommendations to prevent bacterial growth.

What is the difference between GAC and carbon block filters?

GAC (Granular Activated Carbon) filters contain loose carbon granules and offer faster flow rates, making them ideal for whole house systems and fridge filters. Carbon block filters are made of compressed carbon with smaller pores, providing finer filtration but slower flow rates. Carbon block filters generally remove more contaminants and are commonly used in under-sink and reverse osmosis systems.

Do carbon filters remove fluoride?

No, standard activated carbon filters do not effectively remove fluoride from water. If you want to reduce fluoride levels, you'll need a reverse osmosis system or a filter with specialised media such as activated alumina or bone char.

Can I use a carbon filter with hard water?

Yes, you can use a carbon filter with hard water, but the carbon filter will not soften the water or remove limescale. Carbon filters remove chlorine, taste, odour, and organic chemicals — not the calcium and magnesium minerals that cause hardness. For hard water areas, consider using a carbon filter alongside a water softener.

How often should I change my carbon filter?

Most carbon filters should be changed every 6 months or once the litre capacity has been reached, whichever comes first. Check your manufacturer's guidelines for specific recommendations. Regular replacement is essential to maintain filtration performance and prevent bacterial growth in the filter media.