The number on a sediment cartridge is the size of particle it is built to stop. A 5 micron cartridge lets fine silt through but keeps flowing for months; a 1 micron cartridge catches much finer material and blocks up sooner. Choosing between them is a straight trade of clarity against pressure and cartridge life, and the right answer depends on where in the house the cartridge sits.
Nominal and absolute are not the same claim
A nominal rating means the cartridge captures most particles at that size, which is a marketing average rather than a guarantee. An absolute rating means it captures effectively all of them. A nominal 1 micron cartridge can easily pass material that an absolute 5 micron cartridge would hold, so comparing two boxes on the number alone tells you very little. Check which word the manufacturer used before you assume the finer number is doing the finer job.
Where each one belongs in the house
Coarser cartridges belong first, at the point of entry, where their job is to keep grit off everything downstream and to last long enough that you are not changing them constantly. Finer cartridges belong late in the chain, protecting a carbon block or a reverse osmosis membrane where fine particulate would otherwise blind the surface. Fitting 1 micron as a whole-house first stage is a common and expensive mistake: pressure falls off within weeks and the family notices in the shower.
Rust, and why the rating alone will not save you
Sediment ratings only apply to particles. Iron that is still dissolved is invisible and passes through any cartridge no matter how fine, then oxidizes further downstream and stains the fixtures anyway. Penn State Extension sets recommended maximums of 0.3 mg/L for iron and 0.05 mg/L for manganese as aesthetic standards, and treating those means oxidizing first, then filtering. If your cartridges keep coming out orange, you have an iron problem, not a micron problem, and a smaller number will not fix it.
Questions people ask about 1 micron vs 5 micron
Will a 1 micron filter improve the taste of my water?
Rarely on its own. Taste and odor come from dissolved compounds such as chlorine, which need carbon. A sediment cartridge only removes suspended particles.
Does a finer cartridge reduce water pressure?
Yes, and it worsens as the cartridge loads with dirt. Sizing up the housing, or fitting a coarser cartridge ahead of the fine one, keeps the pressure drop manageable.
Can a 1 micron filter remove bacteria?
Do not count on it. Some absolute-rated cartridges reduce larger organisms such as cysts, but disinfection is a job for ultraviolet or chlorination, not sediment filtration.