Before you start to shop for water filters for your home, you need to understand the science behind filter micron ratings.
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.
As all water contaminants are of varying sizes, different water filters have varying micron ratings and are designed to tackle different impurities. In this short guide, I’ll be discussing micron ratings in more detail, providing you with all the info you need in your search for a filter with the right micron size for your needs.
Table of Contents
What is a Micron and How Small is It?
There’s a lot to explore in this guide, but here’s the first thing you should know: the definition of a micron:
A micron is a unit of measurement that’s equal to one millionth of a meter.
To give you an idea of just how tiny this is, the average human hair is about 70 microns across – that’s width-ways, not length-ways. You can measure a red blood cell at around 8 microns – that’s how small we’re talking.
The smallest particles that can be seen by the human eye are around 40 microns, and anything smaller than that would require a microscope to see clearly.
Micron Rating Filtration Spectrum
What is a Micron Filter?
A micron filter is a water filter that’s rated by its micron size. Most filters will display their micron ratings somewhere; it gives customers an idea of how large or small a filter’s pores are, and which contaminants it can tackle.
Filters are incredibly varied in size, with common micron ratings being everything from 0.5 to 100. A typical water filter will fall between the 0.5 and 20 micron ratings.
The smaller the micron rating, the wider range of contaminants, big and small, that can be removed.
But that doesn’t mean that smaller is automatically better.
Larger contaminants like sediment may end up blocking filters with a smaller micron rating, preventing them from being able to filter water through at all. That’s why it’s important to find a filter that can handle the right sized particles for what you’re dealing with.
There are two common micron size ratings to look out for in your search: absolute micron and nominal micron rating.
Absolute Micron Filters
Absolute micron filters are considered the most effective water filtration offering of the two as they’re capable of holding onto one-hundred percent of a particular impurity or set of impurities at a specific micron rating or measurement.
There are several conditions that 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.
Filters with an absolute micron rating are used in scenarios where a particular contaminant must be removed entirely, such as during water sterilization. An example of this type of filter is a pleated filter.
Nominal Micron Filters
The nominal micron rating of filters demonstrates how effectively they can hold onto materials and particulates at a particular micron size. 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 between 60 and 98%.
Nominal rated water filtration systems are those that can remove a lot of chemicals, such as chlorine and its byproducts, as well as some kinds of particulates and impurities that affect taste and odor. Carbon filters are a popular example of nominal micron water filters.
Most Common Micron Ratings
75 microns to 100 microns
The largest micron size you can typically get in 2023, products 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-micron products are some of the larger offerings available. With this higher micron rating, the filtration material has larger pores that allow for the removal of particulates that can be seen by the naked eye, without such a clogging issue.
You can use a filter with 25-micron pores to retain anything that’s bigger than a white blood cell. It should prevent most particulates from being able to access your home’s water system.
A 10 micron rating refers to a filter that can retain a relatively wide range of contaminants like chemicals and metals. However, 10 micron applications won’t work well against bacteria and viruses.
5 micron products can prevent a high amount of impurities from being able to pass through. They’re still not quite tiny enough to handle bacteria, however.
0.5 to 1 micron
Systems of around 1 micron or 1/2 a micron in size are the most effective option when based at the end of a filtration system and used for tackling fine particulates. You could effectively use a 1-micron product for removing bacteria, viruses and other pathogens. However, it may come with some clogging issues.
How Many Microns Should My 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 a specific particle size or size range.
When deciding on how many microns your filter should be, make sure to consider the following things:
What Do You Need to Remove?
If you’re on the hunt for a water filtration solution, you’ve likely got a number of impurities in mind that you want to filter out of your water.
If you don’t already know your water quality, using an at-home test kit (available in hardware stores and online) or arranging for a laboratory test will give you the information you require.
You can then find the filters that have pores of a specific size for handling the impurities in question. If you’re looking to remove tiny bacteria, for instance, 5-micron sediment filter media is no good – you’d require an application that measured at least as low as 1 micron.
To What Level Do You Want it Removing?
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.
Do You Require a Filter With Bigger or Smaller Pores?
Make sure you’re not adopting the mindset of “the tinier, the better”.
A lower micron rating will filter out a much broader spectrum of impurities, but it does come with downsides. You should know, for instance, that because of how these lower micron-rated applications are made, they can often struggle with problems with flow, especially if your water is sediment-heavy.
Smaller micron filters may need to be replaced more frequently, too, because of clogging.
Related: What size micron filter for well water should I use?