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Home » Water Education & Testing » What is a Water Filter Micron Rating?

What is a Water Filter Micron Rating?

By: Craig Smith
Last Updated:
water filter micron rating

When you are looking to purchase any type of water filtration equipment for your home, you will have to familiarize yourself with several different terms that are associated with these types of products.

One of the most important of which is a ‘micron’. That’s because this form of metric measurement directly reflects the effectiveness of any water filtration device’s filter media.

That’s why in this article I will do such things as describe in detail what a micron is, what is a water filter micron rating, and the role this plays in choosing the proper water filter for your needs.

I have dealt with many different types of water filters when working around pool and spa maintenance equipment, so that will help me present this information to you in an easy-to-understand form.

What is a Micron?

A micron is an abbreviated term for a very precise form of linear metric measurement known as the ‘micrometer’. A micron or micrometer equals one-millionth of a meter.

Since this is a very small metric measurement, it makes it highly appropriate for determining how small a particle any type of water filter can reduce or remove.

Usually, this equates to the filter that has the smallest micron pore size being the one that reduces or removes the highest number of tap water contaminants.

It must also be noted that it would be impossible for you to see the smallest micron-sized pores in a water filter and most of the impurities that they can filter out with the naked eye.

That’s because, under ideal circumstances, the human eye can only detect objects that are 29 microns or larger. For comparison’s sake, this is around the size of the point on a small sewing needle.

You will also sometimes see the symbol ‘μm’ used when someone is referencing a measurement that was taken using microns.

Water Filter Micron Rating Chart

Here is a chart that shows the size in microns of several different commonly found impurities in water.

Water Filter Micron Rating Chart

What is a Micron Filter?

A micron filter is a type of water filter where the manufacturer indicates its filtering capability by stating its media pore size in microns. There are two common types of micron filters and these are:

1. Absolute Micron Filters

These are filters that are deemed to be able to remove at least 99% of the impurities in water that are equal to or larger than their stated filter pore size in microns. Even slight clogging over time does not significantly diminish their stated micron rating.

That makes them the preferred choice of filter for sterilization purposes and the final stage in the drinking water filtration process.

2. Nominal Micron Filters

The filtering capability of nominal micron filters is much less predictable than that of nominal micron filters. That’s because they only filter out 60% to 98% of water contaminants that are equal to or larger than their stated filter pore size in microns.

They are not as consistently impactful as absolute micron filters because they are more prone to be impacted by clogging or binding up over time. That’s why these types of filters are mainly used for sediment trapping, pre-filtration, or for enhancing already good quality tap water.

Most Common Micron Ratings

Here are some of the most commonly found micron ratings on water filters and their appropriate uses and the filter media they most often use.

75-100 Microns

This type of micron rating would usually apply to a point of entry sediment filter or some type of pre-filtration filter that’s part of a combination water purification setup. These are usually pleated-type water filters that have large enough pores where clogging is not an issue.

50 Microns

This size micron-rated water filter would be used in the same manner as 75 to 100-micron filters and they are usually pleated style filters too. They will also filter out such water contaminants as human hair and pollen. These also do not clog easily.

25 Microns

This size micron rated filter is used for trapping medium size sediment and they can also eliminate such substances in water as paint, ink, waxes, and some larger types of bacteria. Filters with this size micron rating will usually either be pleated or mesh style and made using acrylic, glass, or Polypropylene fibers.

10 Microns

Ten-micron water filters target such impurities in water as sediment, dirt, red blood cells, and chlorine taste & odor. With this size micron-rated water filter, you will start to see many that are string wound and also contain activated carbon block filtration in them.

5 Microns

Filters with this micron rating target smaller size class V particulates, cryptosporidium, and several types of bacteria. They are mostly made using layered spun materials that consist of activated carbon media or advanced membranes.

0.5 – 1 Micron

If high-quality drinking water is your aim when you are choosing a water filter, then selecting a water filter with a 0.5 – 1 Micron rating is the way to go. That’s because they will filter out the highest number of impurities in water.

These consist of filters that use advanced membranes or extremely dense media in the filtration process.

Normally, most water filter manufacturers will make available the size in microns of the water contaminants that their products can filter out. This information can usually be obtained on a website description of the product or on its packaging.

How Many Microns is Best for Your Filter?

It may surprise you to learn that it’s not always best to buy a water filter with the smallest micron-rated pore size. The reason for this is that the smaller the filter pore size the lower your water flow rate will be and the more often you will have to clean or replace the filter media.

That’s what makes the micron rating of the water filter that you select so important. So, the best way to select a water filtration device for yourself is to purchase a water filter that targets the specific micron size of the contaminates that you want to remove from your tap water.

As an example, giardia cyst particles measure a little less than 10 microns.

So, if your biggest concern with your tap water is to make sure there are little to no giardia cysts in it, then you will only need a water filter that will reduce or remove contaminants that are as small as 5 to 9 microns in size.

Here is another example of targeted water filtration. Say that you want your new water filter to reduce or remove E Coli bacteria. Then you will have to purchase a filter that reduces or removes contaminants that are as small as 0.5 – 1 micron in size.

That’s because E Coli is a long and slender type of bacteria that measures approximately 7 microns in length and 1.8 microns in diameter. The diameter measurement of E Coli is the most important here because that’s the smallest dimension of this particular type of bacteria.

In Summary: It’s Important to Know a Water Filter’s Micron Rating

When you come across a new water filter that you would like to purchase, I would highly recommend that you make yourself aware of what the micron rating of that water filtration device is.

That’s because it will give you a very good idea of the types of impurities in water that it will remove or significantly reduce.

This will lead you to not only selecting a water filter that will produce drinking water that is treated to your desired purity level but that you know will help keep you and your family healthier too.

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Craig Smith
Craig got his start in water working in the swimming pool and spa industry. Water treatment would grow into his main career but he ended up working in the pool industry for over 26 years where much of his time was spent balancing the water in customer's swimming pools and installing water filtration equipment. Craig offers an abundance of water treatment knowledge after helping homeowners get pure water for 26 years.

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