A micron is a unit of measurement describing the pore size of a water filter. The micron rating of a sediment filter determines the contaminants it can remove. Regardless of your water quality, there is a micron filter that is right for you. In this article, John Woodard, our Master Water Specialist, explains the difference between the different ratings of micron filters.
What is a micron filter?
Micron filters remove dirt, debris, and even microscopic particles from water. The pore size of a filter cartridge is measured in microns. The smaller the micron rating, the finer the particulate removed. Which size micron filter you need depends on the size of the smallest particle that needs to be filtered from your water. A 5-micron filter, for example, removes particles as small as 5 microns. Anything smaller passes through the pores. Sediment filters are the most common type of micron filter, but carbon filters can also possess a micron rating. Sediment filters are much like screen doors that allow air in and keep bugs out. However, in this example, the debris blocked by the filter is microscopic.
Learn more: What is a sediment filter?
How small is a micron?
A micron is short for one micrometer, or one-millionth of a meter. The pores of a 20-micron filter are double the size of a 10-micron filter and best for large debris. Any particle smaller than 35 microns is too small to see without a microscope. 25-micron filter and smaller can remove particles that are invisible to the naked eye.
Types of micron filters
Micron filters almost always refer to sediment filters, a type of filter designed to remove dirt, sediment, and other particulates from water. There are many types of sediment filters, each of which excel in different applications. Five major types of sediment filters include pleated, melt-blown, string-wound, bag, and spin-down filters.
Learn more: Types of sediment filters
Pleated filters
Best use: Removing large particles with uniform size
Pleated filters use folded sheets of polyester and polypropylene to filter sediment from water. The folds in these filters give them a large surface area, allowing them to filter more particles at a time. Pleated filters work best with large particles that are uniform in size. The most common micron ratings of pleated filters are between 5 and 25, but you can find some that offer larger and smaller ratings. They are commonly used as reverse osmosis pretreatment or as a whole-house standalone sediment control solution.
Melt-blown filters
Best use: Removing particles that vary in size
Melt-blown filters use depth gradients to trap both large and fine particulate. The core of these filters is denser than the outer areas, meaning the fine particulate that does not get trapped on the outside makes its way to the dense core. The micron rating of a melt-blown filter is the smallest particulate size that it can remove. Because the core traps finer particles than the outside of the filter, melt-blown filters excel at filtering water with particles that vary in size.
String-wound filters
Best use: Removing particles that vary in size
String-wound filters are much like melt-blown filters, but they used string wound around a core instead of polymer fibers. The strings in these filters become denser toward the core, meaning they can filter increasingly fine particulate. Like melt-blown filters, string-wound filters excel at treating water with particles that vary in size. However, string-wound filters must be replaced at east once every six months or when you notice a drop in water quality.
Bag filters
Best use: Applications where high flow rates are needed
Bag filters utilize a bag composed of polyester felt or polypropylene felt to trap sediment. The styles of bag filters vary greatly, and some even feature a depth gradient design. Bag filters vary in micron rating from 1 to 200, and they offer the advantage of high flow rates.
Spin-down filters
Best use: Removing large debris from well water
Spin-down filters use rotational energy to remove sediment from water. Large particles are forced to the outside of the chamber, and a mesh screen removes particulate as small as the micron rating. Unlike the filters above, spin-down filters do not feature a cartridge that must be replaced. Rather, the mesh screen can be cleaned and reused for six to twelve months. The sediment trapped by a spin-down filter must be manually removed by opening an attached valve.
Learn more: What is a Rusco spin-down filter?
Are micron filters reusable?
Some types of micron filters, like pleated filters, can be washed and reused. Pleated filters use thin sheets of polyester or polypropylene to trap sediment as the water flows through the pores. These sheets can be removed, washed, and reused until the structure of the media is compromised. Pleated filters typically must be replaced once every six to twelve months.
Spin-down filters can be flushed and reused because they do not contain cartridges. Rather, the filter screen can be cleaned many times before it must be replaced. The filter screen on a spin-down filter should be replaced once every six to twelve months.
What do micron filters remove?
Because micron rating refers to how large the pores of a filter are, filters with a lower micron rating remove more contaminants than those with a higher rating. Each type of sediment filter is targeted toward specific contaminants that are larger than the pore size of the filter.
50-micron filters
50-micron filters are excellent at filtering contaminants that can be seen by the naked eye. These include large dirt, sediment, rust, silt, and scale particles. These filters do not have many of the clogging issues that smaller micron filters do, making them excellent if large debris is the only thing you wish to remove from your water supply.
25-micron filters
25-micron filters are much like 50-micron filters. However, they can remove smaller dirt particles, sediment, rust, silt, and scale particles than a 50-micron filter. 25-micron filters are also better equipped to remove asbestos particles. The large pore size of 25-micron filters also makes them more resistant to clogging than smaller micron filters.
10-micron filters
10-micron filters are still too large to remove bacteria and viruses, but they remove finer dirt and sediment than 25-micron or 50-micron filters. At this size, filters become more susceptible to clogging. To avoid clogging, ensure you select the right size filter for your water and follow the manufacturer's maintenance instructions.
5-micron filters
5-micron filters remove all of the contaminants larger micron filters can, but they also remove far more silt, some types of mold, certain types of bacteria and cysts, and even more dirt, sediment, and asbestos. Because of the smaller pore size, 5-micron filters are even more susceptible to clogging than 10-micron filters.
1-micron filters
1-micron filters are small enough to remove most types of bacteria and parasites, such as E. coli, Shigella, and Salmonella. These filters also remove extremely fine dirt, silt, asbestos, and other particles. 1-micron filters can reduce levels of Cryptosporidium and Giardia, but they are much less likely to remove them than 0.5 micron filters.
0.5-micron filters
0.5-micron filters remove most cysts and protozoa from water. They are also more effective at removing Cryptosporidium and Giardia than 1-micron filters. Filters that are “NSF 53” or “NSF 58” certified for cyst removal are tested to ensure the removal of these microbes. If you want to purchase the best filter for removing Cryptosporidium and Giardia from your water, search for an absolute filter that possesses one of these certifications.
How many microns should your filter be?
Finding the right micron filter depends on your region and water supply. For example, dirt is fine in New York, so you may need a 1-micron filter or smaller to capture all the fine particulate. Keep in mind that each well or city water supply within a certain region varies.
You should also consider which contaminants you are trying to remove from water. Cysts are parasitic bacteria common in many water supplies that can make you seriously ill. Most city water treatment plants make sure the water is free of cysts, but it is still possible for cysts and other bacteria to get into the city water supply. As a precaution, you may wish to use a point-of-use micron filter, typically 1 micron or less, tested and certified for cyst reduction.
Nominal vs absolute micron filters
Absolute filters have a pore size that measures its exact micron rating. Nominal filters have pores approximately the size of their micron rating. For example, a nominal 5-micron filter could allow a small percentage of 5-micron debris through. An absolute filter is over 95% efficient, which means it shouldn't allow any particles the size of its micron rating through. In an instance where you absolutely must get a certain level of debris out of the water, you should choose an absolute filter over a nominally rated filter. Most micron filters are nominal, but absolute filters are available.
How does pressure drop influence a micron filter?
In micron filters, the pressure drop determines when the filter must be changed. Pressure drop refers to the difference between the incoming filter pressure versus the pressure output. Anytime water flows through media, like in a melt-blown filter or a resin-bonded filter, the water experiences some restriction as it tries to pass through. The pressure drop increases when the filter fills with debris. An increase in pressure drop is a good indication that the filter has reached maximum capacity.
If you have any additional questions, please do not hesitate to contact us.
We have high calcium in our well water, but no sediment. How many microns are calcium particles?
We have had a problem with a very strong rotten egg odour in our water. After some research I installed a filter system with a sediment, iron/manganese and a carbon block filter in that order. I also replace the anode rod in the hot water tank with a Corro-Protect electric anode. This has taken all of the smell out of our water completely.
I am trying to build a filtration system to remove nitrates from ground water under corn fields. What size of microns to I need to keep the nitrates to less than 10ppm? If I understand correctly, ultra filtration is .01 micron; nano-filtration is .001, and reverse osmosis is .0001. But it is not clear to me at what level nitrates would be stopped above 10ppm as required legally. Thank you
Aviva Friedman:
Sulphur Odor could be due to sacrifical rod needs replacement in your water heater. How old is your water heater? If you are handy, you can replace yourself. Or call plumber. We had same problem and have well water to house.
We were getting sulfur odor in the water so Culligan installed a water softener with additional filter (#5) it was fine for 3 weeks but now we’re getting sulfur odor in the water again.
First, what do you think is causing this odor, is it safe to use & what can be done to prevent it?
can you please tackle on oil filtration thank you
If My American plumber W38-PRB Housing Came With A 1 Micron Filter Is That What I Should Stay With Or Could I Sub A 1 Micron Filter Instead?
Very illustrating explanation. Excellent
What a great tutorial on filters. i know now exactly what i need for my home.