Osmio 4.5 x 20 Inch KDF and GAC Filter
KDF and carbon replacement filter for whole house systems
£152.00
Osmio® Whole House Filter Replacement
Osmio 4.5 x 20 Inch KDF and GAC Filter
Replacement KDF and granular activated carbon cartridge for compatible whole house systems, including the Osmio PRO III XL.
KDF and GAC Replacement Cartridge for Whole House Filtration
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Compatible Cartridge:
Designed for compatible 4.5 x 20 inch whole house filter housings. -
PRO III XL Replacement:
Used as one of the main filter stages within the Osmio PRO III XL Whole House Water Filter System. -
KDF Process Media:
Copper and zinc based filtration media used to support chlorine, heavy metal and hydrogen sulphide reduction depending on water conditions. -
Granular Activated Carbon:
Helps improve taste and odour while supporting chlorine and organic compound reduction.
Need the full system? View the Osmio PRO III XL Whole House Water Filter System or browse Replacement Filters.
What Does the KDF and GAC Filter Do?
This cartridge combines KDF process media with granular activated carbon to support whole house water filtration. KDF media works through a redox reaction, where contaminants are changed into different forms as water passes through the media.
Granular activated carbon then helps improve taste and odour, especially where chlorine is present in the incoming water supply. In plain English, KDF helps support and protect the carbon stage, while the carbon helps polish the water for everyday household use.
Buy with Confidence
Your Osmio replacement filter is supplied brand new and backed by the manufacturer’s warranty, with expert support from Regal Flow if you need help choosing or replacing your filter.
Why KDF and GAC Are Used Together
KDF Supports Chlorine Reduction
KDF media is commonly used to reduce chlorine before water reaches the carbon stage.
Carbon Improves Taste and Odour
Granular activated carbon helps reduce chlorine related taste and odour from household water.
Useful for Whole House Systems
The cartridge is designed for point of entry use, helping treat water before it reaches taps, showers and appliances.
Protects Later Filter Stages
KDF media can help reduce fouling and support the performance of downstream filtration media.
The Technology Stage in the Osmio PRO III XL System
The KDF and GAC cartridge is one of the most important treatment stages in the Osmio PRO III XL whole house system. It combines the redox action of KDF media with the polishing ability of granular activated carbon, making it especially useful for taste, odour, chlorine reduction and wider whole house filtration support.
Is This the Correct Filter for Your System?
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Correct For:
Osmio PRO III XL Whole House Water Filter System KDF and GAC cartridge replacement. -
Also Suitable For:
Compatible standard 4.5 x 20 inch whole house filter housings where this cartridge type is specified. -
Not Suitable For:
Small under sink filters, countertop systems, reverse osmosis systems or non standard housings. -
Check Before Ordering:
Confirm the cartridge size, housing size and filter stage before purchasing.
Why Buy from Regal Flow?
Fast, Free UK DeliveryQuick dispatch with no hidden delivery charges.
Expert Product AdviceSpeak to a real water treatment specialist.
Manufacturer WarrantyCovered against manufacturing defects.
Independent RetailerHonest advice across multiple leading brands.
Why This Filter Matters in a Whole House System
A whole house filter has to deal with much higher water volumes than a drinking water filter. That means the media inside the cartridge needs to be suitable for larger flow rates and wider household use.
In the Osmio PRO III XL, this filter works alongside the other filter stages rather than replacing them. Each cartridge has a different job, so replacing the correct stage at the correct time helps keep the system working properly.
KDF and GAC Explained in Plain English
| KDF Media | Copper and zinc based process media that uses redox action to help reduce chlorine, heavy metals, hydrogen sulphide and microorganism build up depending on water conditions. |
| GAC | Granular activated carbon used to improve taste and odour and support chlorine reduction. |
| Why Combine Them? | KDF can help protect and extend the useful performance of carbon, while carbon helps improve the finished water quality. |
| Where It Fits | Used as a whole house filter stage inside compatible 4.5 x 20 inch housings. |
| Main Customer Benefit | Better support for taste, odour, chlorine reduction and whole house filtration performance. |
Why This Cartridge Replaces Separately from Other Filters
The Osmio PRO III XL system uses separate filter stages because each cartridge does a different job. The KDF and GAC filter should be replaced according to its own condition and replacement interval, rather than assuming every cartridge needs changing at the same time.
Complete Your Filter Replacement
The Osmio PRO III XL uses three replacement cartridges, each with a different purpose and replacement interval.
Active Ceramics Filter
Long life filtration stage. Typically replaced every 2 to 3 years.
View ProductKDF and GAC Filter
Supports chlorine, taste and odour reduction while helping protect downstream filtration media. Typically replaced every 12 to 18 months.
Current product
Carbon Block 5 Micron
Fine filtration and activated carbon polishing. Typically replaced every 6 to 12 months.
View ProductReplacement Schedule Advice
Each cartridge works differently, so they should not automatically be replaced at the same time. Replacing the correct filter at the correct interval helps maintain system performance and avoids unnecessary cost.
Replacement and Maintenance Guidance
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Turn Off the Water Supply:
Always isolate the water supply before opening a whole house filter housing. -
Release Pressure First:
Depressurise the housing before unscrewing the sump to reduce the risk of water release. -
Check the Seal:
Inspect the housing O ring before refitting the sump. A poor seal can cause leaks. -
Flush After Replacement:
Run water through the system after fitting the new cartridge to clear loose carbon fines and settle the filter media.
Practical Advice
If your water taste, odour or chlorine smell has changed, this cartridge may be one of the first stages to check. If flow has reduced, also check sediment or carbon block stages, as different cartridges affect the system in different ways.
What Comes With This Product?
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1 x Osmio KDF and GAC Filter:
4.5 x 20 inch replacement cartridge. -
Filter Housing Not Included:
This is a cartridge only, not a complete whole house filtration system. -
Compatible System Sold Separately:
The Osmio PRO III XL whole house system is available separately from Regal Flow.
Downloads & Resources
Compatible System Information
This replacement filter is designed for the Osmio PRO III XL Whole House Water Filter System.
View Compatible System
Replacement Filter Guide
Need help identifying the correct replacement cartridge? Browse our full replacement filter collection.
View Replacement FiltersOsmio 4.5 x 20 Inch KDF and GAC Filter Specifications
| Product Type | Whole house replacement filter cartridge |
| Brand | Osmio |
| Filter Media | KDF process media and granular activated carbon |
| Size | 4.5 x 20 inch |
| Compatible System | Osmio PRO III XL Whole House Water Filter System |
| Compatible Housing | Compatible standard 4.5 x 20 inch whole house filter housings |
| Main Use | Whole house chlorine, taste, odour and filtration support |
| Housing Included | No |
| Standalone System | No, replacement cartridge only |
| Manufacturer Warranty | Manufacturer warranty against manufacturing defects |
Explore More from Regal Flow
Osmio Water Filters and Reverse Osmosis Purifiers
Browse Osmio whole house systems, drinking water filters and replacement cartridges.
View Osmio Collection
Replacement Filters
Find compatible replacement filters for drinking water, reverse osmosis and whole house filtration systems.
View Replacement FiltersFrequently Asked Questions
Is this the same as the Active Ceramics filter?
No. This is the KDF and GAC cartridge. The Active Ceramics filter is a separate cartridge used in a different stage of the Osmio PRO III XL system.
Does this fit the Osmio PRO III XL?
Yes. This cartridge is designed for use as part of the Osmio PRO III XL Whole House Water Filter System.
What does KDF do?
KDF is a copper and zinc based process media that uses redox action to help reduce certain contaminants and support the performance of other filter media.
What does GAC do?
GAC stands for granular activated carbon. It is commonly used to improve taste and odour and to help reduce chlorine from water.
Is the filter housing included?
No. This product is the replacement cartridge only. The housing or complete whole house filter system is sold separately.
Can I install it myself?
Whole house cartridges must be changed carefully. The water supply should be isolated, pressure released and the housing seal checked before refitting. Many customers choose to use a qualified plumber.
Need Help Confirming the Correct Osmio Filter?
If you are not sure whether this is the correct cartridge for your Osmio PRO III XL system, contact Regal Flow before ordering. We can help you check the filter stage, housing size and replacement schedule.
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