Water sediment is any solid the water is carrying: sand and silt from a well, rust flakes from old galvanized pipe, scale shed by a water heater, or the fine particles a utility stirs up when it flushes a main. The color, the timing and where in the house it appears usually identify it, and the identification matters, because two of those causes are filtered and two of them are repaired.
Read the sediment before you filter it
Catch a sample in a clear glass and let it stand. Coarse sharp grains that drop fast are aquifer sand, which points at the well screen or a pump set too low. A fine tan or grey cloud that takes hours to settle is silt or clay, common after heavy rain in a shallow or poorly grouted well. Orange flakes are oxidized iron, either from the water or from the inside of steel pipe. White or grey chips are hardness scale, usually shed by a water heater or a length of badly scaled line.
When it is the well, not the water
Sand appearing suddenly, or getting worse over a season, is a well problem rather than a filtration problem. A failing screen, a pump drawing from too near the bottom of the borehole, or a casing breach after ground movement will all send grit into the house, and a cartridge filter simply becomes a consumable that hides the fault while the pump wears out. Private wells are not federally regulated under the Safe Drinking Water Act, so nobody flags this for you. Sudden sand is a call to a well contractor first.
When it is the plumbing
If sediment shows only at the hot taps, the water heater is the source: scale and corrosion accumulate in the tank and break loose, and flushing the tank on a schedule fixes it. If it shows only at one fixture, the aerator or the fixture supply line is holding debris left over from a repair. If it appeared right after the utility worked in your street, it is main flushing, and running an outside spigot until it clears is the whole remedy. None of these three need a filter bought for them.
What treatment sediment actually needs
Genuine, continuous sediment in the incoming supply is handled in stages: a spin-down separator to strip the coarse grit and be flushed without a cartridge change, then a cartridge or backwashing filter to catch the fine material. Sizing is by flow and by particle size, not by the diameter of the housing, and putting anything too fine on the front of the house buys pressure loss and weekly cartridge changes. Our best sediment filter for well water guide sets out how the stages are matched.
Questions people ask about water sediment
Why is there sediment only in my hot water?
The water heater is shedding it. Scale and corrosion collect in the tank and break loose, so flushing the heater on a regular schedule is the fix, not a filter.
Is sediment in well water harmful?
The particles themselves are usually a nuisance rather than a health issue, but silt arriving after rain can mean surface water is reaching the well, which is worth testing for bacteria.
Will a sediment filter stop sand from my well?
It will catch it, but sand from a well normally means a screen, casing or pump-depth problem, and the filter is only masking wear that is happening to the pump.
Why did my water go cloudy after the town worked on the street?
Main flushing and repairs stir up settled material in the pipes. Run an outside tap until it clears, then check the aerators on your fixtures for trapped debris.