A one micron sediment filter is fine enough to catch silt well below what the eye can see, and on a private well that makes it valuable in one particular position and a poor choice in another. It is a finishing stage. Put first on a well carrying grit, it blinds within weeks and costs the house pressure for no benefit.
What it catches on a well
Fine silt and clay that a coarser cartridge passes, precipitated iron particles left by an oxidizing stage upstream, and the fine fraction of sand that a separator misses. In an absolute rated version it is also claimed against protozoan cysts such as cryptosporidium and giardia, which matters on shallow, dug or spring fed sources that may be under the influence of surface water. Nominal and absolute ratings are printed identically on the shelf and mean very different things, and only absolute supports a cyst claim.
What has to come before it
On any well producing visible solids, a centrifugal separator or a backwashing media tank goes first, taking out the grit that would otherwise consume a fine cartridge in days. Then a coarse cartridge takes the bulk of the remaining silt. Only then does a one micron element make sense, dealing with what got through rather than with everything. This staging costs one extra housing and multiplies the life of the expensive cartridge several times over, which is why it is standard practice on wells.
What it does not do
Nothing dissolved is affected. Hardness, dissolved iron before it has been oxidized, manganese, tannins, nitrate, arsenic and sulfur smell all pass through a one micron cartridge unchanged. It does not disinfect either: bacteria and viruses are considerably smaller than one micron and are not retained. Where it does serve disinfection is as the stage immediately before an ultraviolet chamber, since UV only inactivates organisms in water clear enough for the light to reach them, and turbidity shadows them from the lamp.
Sizing it so the well can live with it
Use a big diameter housing, since a slim one at this rating will not sustain household flow on well sediment for long. Watch the pressure drop rather than the cartridge's appearance, because a fine element blinded by silt often looks nearly clean, and fit gauges either side so the change is measured rather than guessed. Remember that a well system cycles pressure every time the pump starts, which works the housing harder than a municipal supply. Our sediment filter guide covers matching the staging to a well.
Questions people ask about 1 micron sediment filter
Can a one micron cartridge go first on a well?
Not on a well producing solids. It blinds within weeks. Put a separator or coarse cartridge ahead of it and use it as a finishing stage.
Does it remove cysts?
Only in an absolute rated version. Nominal ratings capture most particles at that size but do not support a cyst reduction claim.
Will it help with iron in well water?
Only iron already oxidized into particles. Dissolved iron passes straight through and needs an oxidizing stage first.
How do I know when to change it?
By pressure drop, measured with gauges either side. A fine cartridge blinded by silt frequently still looks nearly clean.