A 20 micron water filter is a coarse sediment element, sized to catch sand, grit, rust flakes and scale chips while letting fine silt and everything dissolved pass through. It is a protective stage rather than a purifying one. Used first in a train it takes the heavy load off finer cartridges; used alone it will disappoint anyone expecting cleaner tasting water.
What that rating covers
A micron is a thousandth of a millimeter, and the human eye stops resolving individual particles somewhere around forty of them, so a twenty micron element sits just below what you can see. In practice it stops sand grains, coarse silt, rust and scale flakes shed by old pipe, pieces of pipe dope and the debris that follows mains work or a well pump repair. It will not stop fine clay turbidity, which stays suspended and passes through, and it does not touch anything dissolved. Most household cartridges at this size are nominal rather than absolute, meaning they capture most particles at the rating rather than every one, so treat it as a bulk stage rather than a barrier.
Why the coarse stage goes first
Filter trains are built so the cheap stage protects the expensive one. Put a coarse element at the front and it takes the bulk of the solid load, so the fine cartridge behind it stays clean and lasts, and the carbon tank or softener resin further along never sees the grit that would foul it. Reverse the order and the fine element blinds off in days while the coarse one behind it sits idle. A common household arrangement is a spin down screen or a coarse element first, then a finer one, then whatever treatment the water actually needs. Skipping the coarse stage does not save money, it just moves the cost to the cartridge you change most often.
Choosing between twenty and something finer
Pick the rating from what your water carries, not from a wish for the smallest number. Well water that visibly runs sandy after the pump starts wants a coarse element in front, because a fine one will clog before the week is out. City water that only occasionally shows debris after mains work can usually run a finer element on its own. If you can see particles settling in a glass, start coarse. If the water looks clear but aerators keep blocking, a finer polishing stage behind the coarse one is what you need. Watch pressure across the housing and let the change interval, rather than the label, tell you whether you chose right.
What a sediment filter cannot make safe
Solids are all this stage removes. Bacteria, nitrate, arsenic, lead, hardness and dissolved iron all pass through a twenty micron element without being slowed. That matters most for private wells, which the EPA notes are not federally regulated under the Safe Drinking Water Act and which serve around 15 percent of the US population, over 43 million people. The EPA also cites a USGS study of 2,100 private wells in which about one in five carried at least one contaminant above a human health benchmark. Clear water is not tested water, and our well water testing guide sets out what to have measured before choosing any treatment beyond sediment.
Questions people ask about 20 micron water filter
Is a 20 micron filter fine enough for drinking water?
Not on its own. It removes visible grit but nothing dissolved and no microorganisms, so drinking water treatment needs carbon, a membrane or disinfection behind it depending on your test results.
Should I run 20 micron before or after a 5 micron element?
Before. The coarse element takes the bulk of the load so the fine one lasts, and reversing the order simply clogs the fine cartridge while the coarse one does nothing.
How often does a 20 micron cartridge need changing?
Whenever pressure drop across it climbs noticeably, which depends entirely on how dirty the water is. Gauges either side turn that judgment into a reading rather than a guess.
Will a 20 micron filter stop my water looking cloudy?
Only if the cloudiness is coarse suspended solids. Cloudiness that clears from the bottom up within a minute is trapped air, and fine clay turbidity needs a much finer stage.