RO, DI, HMA, KDF, UV, Activated Carbon -- What Are These Water Filtration Terms About?

Water filtration is a complex subject in itself, and it can sometimes sound even more complicated because of the frequent use of various acronyms employed by specialists and sellers. RO, DI, UV, HMA, KDF? Read on and find out what these mean.

Today’s article will explain and clarify the most commonly found water filtration acronyms.

RO stands for Reverse Osmosis…

and  describes one of the most popular water purification methods. It is (just as the name suggests) the opposite of the natural process of osmosis where water naturally moves through a semipermeable membrane from a low ion concentration to a high ion concentration.

When pressure is applied to the more concentrated -- less pure -- side of the  semipermeable membrane, water molecules move through the membrane to the low ion concentration -- purer -- side.

Reverse Osmosis (RO) filters available on the market simply use mains water pressure to accomplish the process. Usually such a filter is used in combination with other filters, creating a RO water purification system that will remove up to 99% of contaminants from water.  The RO membrane in a typical filtration system requires replacing every few years.

DI stands for Deionisation…

… and is also sometimes described as Ion Exchange, Strong Acid/Strong Base, Polishing, or even “Nuclear Grade”. This process removes all ions from water using the process of ion exchange.

Deionisation filters do not utilise physical filtration in which  impure water passes through pores and thus cannot remove bacteria or particulate contaminants, for which other filters are needed. However, as most of non-particulate impurities in water are actually dissolved salts (often referred to as Total Dissolved Solids -- TDS), deionisation used as part of a filtration system produces very pure water, similar to distilled water, but faster, and cheaper.

The process uses deionisation resins, and as they get used up over time, DI filters in a typical filtration system require replacement of the resins every six months.

HMA stands for Heavy Metal Axe…

...and is a commonly used name for a filtration system (often constructed from a combination of RO and DI filters) that removes or greatly reduces heavy metal contamination from the water, which is of particular concern for keepers of aquarium fish.

KDF stands for Kinetic Degradation Fluxion...

...which is a copper-zinc formulation that uses the oxidation/reduction process for removal of chlorine, lead, mercury, iron, and hydrogen sulphide from water. This method of water purification has also some anti-microbial effect, but is mostly used in combination with other techniques to remove chemical contaminants. Unlike some other methods, KDF is also effective at higher water temperatures and can thus be used for shower and bath water filtration.

Activated Carbon…

…also known as active carbon, or activated charcoal is carbon that has undergone processing that hugely increases its porosity -- a single gram of activated carbon can have as much as 500 square metres surface area available for adsorption and chemical reactions that bond impurities from the water that passes through.

Filters using activated carbon are a popular, economical and effective water purification technique used in water filtration, from simple jug filters to sophisticated multi-stage filters.

UV stands for Ultra-Violet…

...and is used for removal of disease-causing microorganisms (bacteria, viruses, fungi etc. ) from water. UV lamps are incorporated into the water supply system, producing water that is microbiologically safe.

Tap water in the UK is normally microbiologically safe, but if you need a water purification system for a property with a private water supply (for example a holiday home in a remote area, or any other supply that uses ‘’raw water’’), sterilisation with UV light is something to consider.

Any system that uses UV lamps will still require mechanical filters to remove particulate matter, so the UV light can operate most efficiently and the microorganisms cannot ‘’hide’’ from the light among the solids present in the water.


The variety of purification techniques present on the market can seem baffling. The best way to choose the optimal water purification system for your needs is to discuss your specific situation with a filtration specialist, who will be able to recommend the best solution, whether you need filters for drinking water, aquarium fish or window cleaning.

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