A 20 micron cartridge is a workhorse: it catches sand, grit and rust flakes, holds a lot of dirt and keeps the pressure up for months. A 5 micron cartridge captures much finer silt and the cloudiness you can actually see, but it loads far faster on the same water. On most well supplies the answer is not to choose between them.
What the gap between the two ratings buys you
Between 20 and 5 micron sits most of what makes water look hazy: fine silt, clay and oxidized iron particles. A 20 micron cartridge lets that through and stays open; a 5 micron cartridge holds it and slowly blinds. Dirt capacity, not the rating, decides how often you are down there with a wrench, and a pleated cartridge with a large surface area at 5 micron can outlast a spun cartridge at 20 micron on the same well. Compare surface area as carefully as you compare the number.
Stage them instead of choosing
The standard arrangement on a dirty supply is two housings in series: 20 micron first to take the heavy load, then 5 micron to polish what got past it. The coarse cartridge protects the fine one, so both last longer than either would alone, and pressure drop stays sane. Use a big-blue sized housing rather than a slim one wherever flow matters, and fit a pressure gauge before and after the pair so you can see a cartridge loading up instead of waiting for the shower to tell you.
Well owners: match the rating to what the well throws
Nobody sets this specification for you. The EPA notes that private wells are not federally regulated under the Safe Drinking Water Act, and that around 15 percent of the US population, over 43 million people in more than 23 million households, rely on them. That means the owner decides. Catch what your well actually produces: sand after a pump cycle, silt after heavy rain, or orange particles that mean iron rather than dirt. Our well water testing guide sets out what to sample before choosing cartridges.
Questions people ask about 5 micron vs 20 micron
Will a 5 micron cartridge cut my water pressure?
It will drop pressure more than a 20 micron cartridge, and much more as it loads with dirt. A larger housing or a coarser cartridge ahead of it keeps that in check.
How often should sediment cartridges be changed?
There is no fixed interval; it depends entirely on how dirty the water is. Fit gauges and change on pressure drop rather than on the calendar or on guesswork.
Is a washable pleated cartridge worth it?
On a well that throws sand, yes. A rinsable pleated cartridge as the first stage can be cleaned several times before replacement, which cuts running costs noticeably.