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How Many Microns Should Your Water Filter Be?

Posted by Brock Robinson on July 08, 2019

A micron is a unit of measurement describing the pore size of a micron water filter. Sediment filters remove different contaminants depending on their micron rating. John Woodard, our Master Water Specialist, explains the difference between a .1-micron, .5-micron, 5-micron, or 10-micron filter.

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 filtering 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. Sediment filters are similar to screen doors that allow air in and keep bugs out, except the debris blocked by the filter is microscopic. 

how small is a micron?

Learn more about sediment filters

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. The particles filtered from a 25, or 20, or 10 are invisible to the naked eye. 

How many microns should your filter be?

Finding the right micron filter depends on your region and water supply. For example, dirt is super 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'll also want to consider what you're trying to remove from the 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's possible for cysts and other bacteria to get into the city water supply. It's a good idea to use a point-of-use micron filter, typically 1 micron or less, tested and certified for cyst reduction. 

micron size chart

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 there 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 have to 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 it's time to change the filter. 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.

Comments 1-10 of 19

We have high calcium in our well water, but no sediment. How many microns are calcium particles?

Michael Walsh on March 27, 2023

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.

Mike on February 03, 2023

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

Jim Lohr on March 28, 2023

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.

Alan Thomas Slater on August 11, 2022

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?

Aviva Friedman on July 13, 2022

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?

Francine Fowler on December 30, 2021

Very illustrating explanation. Excellent

Rafael on October 13, 2021

What a great tutorial on filters. i know now exactly what i need for my home.

curtiss K cole on February 03, 2021
Is it better to use 0.5 micron instead of 1 micron?
Carol on September 21, 2020
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