Richard Arconti 
You want to choose the best water filter for your home, and one of the most important factors to consider is micron rating. This rating measures what size of particles a given filter can capture and what is small enough to pass through the filtration media.
Therefore, micron rating is a crucial metric for determining what your filter can keep out of your water. For example, a filter capable of trapping sediment may not be able to eliminate something as small as bacteria.
Various water contaminants come in a wide range of sizes. Every home has different filtration needs, water filters come with different micron ratings intended for different applications. This guide will explain what micron ratings are and what you need to know to choose the correct filter.
What Is a Micron Filter?
Micron filters remove debris, dirt, and even microorganisms like bacteria and viruses from water. The size of the pores in a cartridge filter is measured in microns. This determines the particle size that a filter will allow to pass through. A smaller micron rating will remove finer particles.
However, micron filters come in a wide range of sizes. With common micron ratings up to 100 to filter visible sediment and down to 0.1 to remove bacteria and viruses. For example, if the average bacteria is .75 microns in diameter, a micron rating of .75 or lower will remove it.
The size of the filter you need will depend on the smallest particle that needs filtering in your water. Although a finer filter traps a wider range of particles, many mistakenly believe they are simply better.
Sediment filters with a smaller micron rating face a higher risk of clogging, meaning they will not filter any water. This will lead to frequent filter replacements and reduced water pressure. That underscores why choosing the right micron-sized filter for your application is crucial.
How Small Is a Micron?
A micron rating refers to the size of particles that a filter is capable of capturing in the pores of its surface measured in microns. The term “micron” is an abbreviation of micrometer, wherein one micron is 1/1,000,000th of a meter (or 1/25,000th of an inch).
This means that a micron is so small that it cannot be seen by the naked eye. To put this size into perspective, a single strand of human hair is between 40 to 90 microns in width. Even a blood cell may range from 7 to 8 microns.
Although particles less than 50 microns aren’t visible to the naked eye, they should still be filtered from your water. This means that the question is, how many microns should your filter be capable of capturing?
How Many Microns Should My Filter Be?
The fact is that no single micron rating is correct for every application. There is a wide range of micron ratings because there are just as many different sizes of contaminants. For large debris, a sediment pre-filter with a 75 – 100 micron rating may be enough. If the particulate is super fine, a micron rating of 1 or smaller could be necessary. For microorganisms and cysts, a sub-1 micron rated point of entry filter is generally required.
Here are the key considerations to know how many microns your filter should be:
- What do you need to remove: Testing your home’s water is the surest way to understand exactly what contaminants need to be addressed. Other resources to see your water quality include checking the EPA Water Quality Reports or EWG Database.
- Smallest is not best: It may seem easiest to select the filter with the lowest micron rating, but this is often a poor decision. A filter with a finer micron rating may remove both the smallest particles and the larger contaminants, but this can cause it to clog quickly. As a result, your water pressure will plummet and you will need to change the filter frequently.
- Filter replacement life: The quality of your water will determine how long a filter will last. If your water is heavily contaminated, the filter will need to be replaced more often. Take into account the ongoing maintenance cost when deciding on the right sediment filter.
Types of Micron Water Filters
Water filters come with two types of micron ratings, either absolute or nominal. These terms are used to distinguish how effective a given filter is at removing particles of the micron size it is rated for.
Absolute Micron Filters
An absolute micron filter is a gold standard for water filter ratings, indicating that a filter will remove 100% or more of particles of that micron size. This means that if a filter has an absolute rating of 1 micron, it will remove 100% of particles of this size. For example, a filter with an absolute pore size of 1 micron that is certified to NSF Standard 53 or 58 will effectively treat cysts in your drinking water.
Nominal Micron Filters
Nominal micron filters are less guaranteed to remove a particular size of particle and instead show an approximate size of the particles that a given filter can remove. In most cases, these filters may remove the particles they are rated for, but their effectiveness varies. Generally, water filters with a nominal rating are capable of removing between 60% and 95% of rated contaminants, and they remain a highly popular and effective option.
Nominal rated water filters are used to remove particulates, chemicals, and chlorine, as well as bad taste and odors.
Most Common Filter Micron Ratings Available
Micron rated water filters vary in shape, size, and the material used to make the filter. Below is a summary of common micron ratings available and what they are best at removing.
100 Microns
This is the largest micron size available among widely purchasable filters. A 100 micron filter will remove large sediment clumps at system entry points. These are typically used for pre-sediment filters for whole home water filters.
50 Microns
Another of the larger particle-sized filters on the market, a 50-micron filter retain particles visible to the naked eye. These 50 micron sediment filters will remove sand, silt, and are especially ideal for well water with heavy iron.
25 Microns
If you want a fine filter that can keep out anything larger than a white blood cell, look at 25-micron options. A 25-micron water filter will remove particles invisible to the naked eye and keep most foreign particles from invading water flows.
10 Microns
A filter that limits to 10 microns is best for eliminating chemicals, metals, and other undesirable contaminants from your water system with ease–only bacteria and viruses are not removed. The 10 micron vs 5 micron filter is still generally considered a pre-filter. Whereas a 5 micron filter will begin to remove finer particles.
5 Microns
Much like 10-micron filters, ones with a 5-micron rating will block almost all impurities from the water flow, but again, they cannot prevent bacteria from slipping through.
1 Micron
Filters with a 1-micron rating are some of the finest and most purifying on the market since even bacteria, viruses, and similar contaminants cannot pass through them. A filter with a micron rating of less than one is typically part of a multi-stage system where larger particles are already removed. Any system relying on them must take caution to prevent clogs, however.
.5 Micron
This is among the finest micron rating you will find for filters widely available for purchase. Much like 1-micron filters, these will cut out all foreign contaminants, including bacteria, viruses, and cysts. The downside is the elevated risk of clogging if preventative measures aren’t taken
Is Higher Or Lower Micron Better?
Different ratings of filters are designed for different filtration needs. Higher micron ratings are better suited for large debris and sediment. Smaller micron-rated water filters are best for removing microorganisms and very fine particles.
Selecting the correct filter relies on knowing what particles need to be filtered out in your system. There are filters designed to eliminate those contaminants from visible sediment to bacteria and pathogens.
Does Micron Rating Affect Water Pressure?
The micron rating of a water filter indicates the size of the pores in the filtration media and, as a result, the restriction it poses to material passing through. This means that filters with a lower micron rating will create a greater restriction which can affect water pressure.
However, as long as the filtration system is chosen with your home in mind, it will generally be mild, and if pressure drops, this often simply indicates that it is time to replace the filtration media.
