Water Filters

Coming in all shapes, sizes and systems, there are such a variety of water filters out there it can be confusing to know which is best for your needs. You may even already have one in your home! Luckily we will always be able to give the best advice on the water filters you need. 

What does a water filter do?

Water filters can be  used separately or in combination to deal with different water issues in homes and businesses. They can be used to improve taste, to protect equipment or to remove contamination. One of the main reasons that people have a water filter in their home is to stop the scale build up in their kettle. But what does the filter actually do? The best way to explain is to look at the different methods of filtration and how they work.

Methods of filtration


The simplest water filter to understand, this is a physical barrier which catches sediment and particles. These types of filters can vary from simple screens and string filters to complex ceramic units. They are measured and rated by the size in microns of the particles they can trap. For example, a typical string filter would be measured at 5 microns which would remove visible size debris. A filter measured at 0.5 microns can remove cysts. One thing to note is that the finer the filter, the slower the flow of the water will be.


One of the most common filters, these normally use carbon (GAC) which is a great material due to its large surface area. These filters are useful in removing the chlorine which causes the bleach flavour that many people complain about in their drinking water. Chlorine is put into the water at source to keep it safe however so it is very important that if we remove it, we consider the safety of the water. We would therefore never recommend that chlorine is removed before water is stored, much better that it is removed just as it leaves the tap.


In science terms, this means to isolate a substance chemically. In the water industry, we can use polyphosphates to sequester calcium and magnesium and (less commonly) iron. As we know, it is the calcium in the water supply that causes scaling issues across much of the UK. The polyphosphate does not remove the ‘hardness’ as such but instead tries to keep it in a solution, stopping it from forming scale deposits. Sadly sequestration becomes less effective as water temperature increases, with temperatures above 95 degrees being ineffective. It is instead a far more efficient and effective method to soften water using the ion exchange process in traditional salt based water softener machines.

Ion Exchange

Whilst there are several versions of ion exchange, they all use a polymer matrix resin material. This looks like fine sand and is held in storage tanks that your water passes through. Unlike sequestration, ion exchange physically removes the ‘hardness’ minerals, trapping them in the resin. The resin is then regenerated using a backwash made from brine (salty water) which cleans the material ready for reuse. Because salt is used in this process, we need to be conscious of the salt content of the water (which regulations state must be kept below 200 ppm). For most of the country this is not a problem however and, even in those places where it is, we can easily manage it. This brings us to our next type of filtration….

Reverse Osmosis 

This system is always combined with other filtration methods but in itself removes dissolved inorganic solids by forcing water through a semipermeable membrane under pressure. This allows the clean water to pass through, leaving the contaminants behind. It is by far the best solution for pure drinking water and when as engineers we are confronted with challenging drinking water, it is our go to. The system is normally installed at point of use and may have a small storage tank, extra filters or a small pump to make it more efficient. Many Reverse Osmosis systems these days also include a ‘remineralisation’ filter. These put a small amount of mineral back into the water after it has been filtered. This can be beneficial in tea and coffee making or for giving the water a nicer flavour. Most Reverse Osmosis systems (when combined with a water softener) will legitimately claim to remove 99.9% of contaminants (pumped).

Which water filter do I choose?

The main question is what do you want to achieve?  Many people in the UK struggle with hardness in their water supply that damages their homes. The best method for removing those damaging minerals is a whole house, ion exchange water softener. Installed by the incoming water main, this will protect all of your home. You will also need to consider what other water we might want in your home. Ideally for the garden we would not treat it at all and preferably use rain water. There are a few options when it comes to your drinking water however. Your local AIWSE expert such as ourselves will be able to guide you through these but here are some typical examples used in the industry:

Inline Systems 

These are typically used at point of use (usually your kitchen sink) and are designed to remove sediment and bad flavour. You can also find them on commercial equipment. It is important to ensure that the filter is the correct one for the job at hand as there are various different types available. In a home environment they are normally paired with a small secondary drinking water tap or a combined 3 way tap.

American Style Fridges

These filters come in a vast range of sizes and fittings but can often be an inline filter hidden behind a unit. It is very important to maintain these filters to keep your fridge functioning as it should. Your local AIWSE member will be able to help you find the correct one for your needs.

Coffee Machines 

This is a very specialist area as coffee roasters have discovered that to brew the very best drink, it is important that the water has the correct chemistry. This means that they actually need some minerals to be present in the water, just not enough to damage the equipment. It is becoming increasingly popular for AIWSE members to install a water softener to protect the building and then a Reverse Osmosis unit to give the final high quality water for the coffee making. If you need help and advice then always speak to a professional from the AIWSE before you invest in a system.


These are of the type of filters where the filter screws or drops into a housing. These can be made from a variety of materials and can come in lots of different types and sizes. Most Franke and Britta taps use this method of filtration but your AIWSE member should be able to supply a suitable replacement. 


In the industrial world, water is used in all manner of processes. From the dentist drill, laser cutting and food production to steam ovens and mould making, the list is endless. All of these require specialist water treatment knowledge to specify the correct equipment and to maintain it. Make sure you use an expert on your next project and contact your local AIWSE member first. 

What about a jug filter?

One of the most common filters found in households over the past few years have been jug filters, often from a company such as Britta.The average ‘Britta’ jug has a combination of carbon, polyphosphates and ion resin, usually to keep just your kettle clean. A big problem with these jug filters is that most people forget to change the filters plus leaving a jug of water on the side in a warm kitchen is questionable from a hygiene perspective. As you can see from above, there are so many far better solutions you can have installed that will save you time and money.

Do you want perfect water?

If you are unhappy with your water quality, contact us today. We have the answer to your problems.

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