What is Micron Rating & Why Micron Size Matters for Water Filters?

When you’re looking at a water filter, you’ll likely come across amongst the technical specifications, each filter has a micron rating. But what does a micron rating even mean and why you should care about it?

In this blog, we will discuss everything you should know about micron ratings and tips to select the best filter for your home based on micron rating.

What is a Micron Rating?

To understand what a micron rating is we first need to understand what a micron is.

A micron is a metric unit of measurement, also known as a micrometre, a micron is a millionth of a metre or a thousandth of a millimetre. It is denoted with the symbol: μm.

Anything roughly below 40 microns in size is invisible to the naked human eye and would require a microscope to see it.

The micron size of a water filter, otherwise known as a micron rating, will determine what size particles it’s capable of trapping, and which particles may be small enough to pass through.

The smaller the micron rating, the finer the particulate removed. A 5-micron filter, for example, removes particles as small as 5 microns. Anything smaller passes through the pores.

Absolute vs Nominal Micron Filters

Filters work in different ways to filter contaminants. The amount that will get removed during water filtration depends on whether a nominal or absolute filter is used.

Absolute Micron Rating

An absolute rating refers to the largest particle that will fit through the filter, so a 1-micron absolute filter should prevent anything larger than 1 micron from passing through 95% of the time.

Just as its name would signify, an absolute micron rating retains 100% of particulate at a specified micron rating. Several conditions need to be in place for an absolute micron filter to effectively work, including the water pressure, the concentration of contaminants, the particle size or diameter of the impurities, and even the method used by the filter to identify the impurity.

An example of this type of filter is a pleated filter.

Nominal Micron Rating

A nominal filter gives an indication rather than a guarantee of the size of particles that will pass through, with some of the pores or holes in the filter surface being larger than the rated size, they will let a percentage of particles through that match the micron rating.

Different water filters have varying levels of effectiveness depending on the material used to manufacture the filter system, the testing method and environment, and the concentration of the impurities in question. Usually, a nominal micron rating for a filter will remove be between 60 and 98%.

Nominal rated water filtration systems are those that can remove a lot of chemicals, such as chlorine and chloramine, as well as some kinds of particulate and impurities that affect taste and odour.

Carbon filters are a popular example of nominal micron water filters.

Most Common Micron Ratings

As all water contaminants are of varying sizes, different water filters have varying micron ratings and are designed to tackle different impurities.

75 microns to 100 microns

Water filters with a 75-100 micron rating are often used at a home’s point of entry to eliminate large sediment particles from well and city water supplies.

50 microns

50-micron water filters have larger pores that allow for the removal of particulates that can be seen by the naked eye, without such a clogging issue.

25 microns

Filters with 25-micron pores can be used to eliminate anything bigger than a white blood cell. It should prevent most particulates from entering your drinking water.

10 microns

A 10-micron rating refers to a filter that can retain a relatively wide range of contaminants like grit, sediment, chemicals and metals. Generally, they are used as sediment filters and can be made of wound or pleated polypropylene.

5 microns

A 5 micron rated water filter helps to remove sediment, silt and anything that is 5 microns in size and bigger.

1 micron

Systems of around 1 micron in size are the most effective option when based at the end of a filtration system and used for tackling fine particulates.

How many microns should your filter be?

There is no universal filter micron rating that works best across the board. Different filtration cartridges have different micron sizes for a reason: because they’re intended to retain and remove impurities of specific particle size or size range.

When deciding on how many microns your filter should be, make sure to consider the following things:

Know What Your Are Removing

Knowing what is in your water is the first step in determining what micron rating the water filter has to be.  Water filters with different micron ratings are able to remove a range of contaminants such as sediments, chlorine, fluoride, heavy metals etc.

If you’re looking to remove tiny bacteria and viruses, then probably a UV filter is your best option. Similarly, if you want to remove excessive hardness in water, then a water softener is the ideal solution.

Level of filtration required

Nominal filters are pretty effective at contaminant removal, while absolute filtration will allow for the removal of 100% of the problem impurity.

That means you’re always going to get much better results with absolute filtration. Again, there’s no right answer here, as you may not be looking to eliminate the full amount of impurities from your water.

Smaller isn’t always better

A lower micron rating will filter out a much broader spectrum of impurities, but it does come with downsides. Smaller micron filters can often struggle with problems with flow, especially if your water is sediment-heavy and may need to be replaced more frequently, too, because of clogging.

To ensure there is little to no flow loss, a filter with a higher micron rating or a larger pump is required.

Choose a Reverse Osmosis System

Reverse osmosis systems involve a multi-step filtration process that uses a combination of different filtration media with different micron ratings to eliminate contaminants of all micron sizes such as sediments, silt, heavy metals, fluoride, chlorine, pesticides, cysts etc.

As an example, our popular Ecosoft 5 stage reverse osmosis system uses 5 different stages to purify water.

Stage 1 involves polypropylene sediment pre-filter with a 5-micron rating removing large particles of mechanical impurities (silt, sand, rust, scale).

Stage 2 involves a granulated activated (GAC) filter with a 10-micron rating removing chlorine and other organic compounds from water to improve taste and remove any odours present.

Stage 3 is another polypropylene sediment pre-filter with a 1-micron rating that removes fine mechanical impurities which may have passed on from 1^st stage.

Stage 4 is the semi-permeable membrane which at the molecular level removes everything from the water including cryptosporidium bacteria and cysts.

Stage 5 is usually a post-carbon filter that acts as a polishing agent and eliminates dissolved gases in the water.

Some reverse osmosis systems like our Ecosoft 6 stage system, Stella reverse osmosis system, and Ecosoft PURE AquaCalcium system also enrich the drinking water with healthy minerals by adding an extra remineralizing filter as the last filtration stage.

If you are on a public water supply, then a reverse osmosis system is probably the best way to get the highest quality drinking water possible.

Celtic Water Solutions has nearly 20 years of rich experience in water treatment for both residential and commercial clients and we are confident in our ability to improve the quality of drinking water in your home.

If you need more information on any of our drinking water systems, then feel free to get in touch with our team of experts.

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