A sediment filter is a mechanical pre-filter that strains sand, silt, rust, and other solid particles out of water. It uses a spun, pleated, or string-wound cartridge rated in microns. Placed ahead of softeners, carbon filters, and reverse osmosis, it protects that equipment and your fixtures from grit.
Not everything in water is dissolved. Some of it is solid grit you could see under a lens. Sand, silt, clay, and flakes of rust ride along in the water. They can clog valves, scratch fixtures, and ruin finer filters. A sediment filter is the first line of defense. If your tap water runs cloudy or gritty, it is often the fix.
Micron Ratings
A sediment filter is rated by the size of particle it can trap, measured in microns. A 10-micron filter traps particles about 10 microns across or larger. For comparison, silt runs from about 2 to 50 microns, and sand starts near 50 microns. The rating comes in two styles. A nominal rating traps roughly 85 percent of particles at that size. An absolute rating traps about 99.9 percent. Absolute filters cost more but protect sensitive gear better.
Types of Cartridges
The most common style is a spun or melt-blown cartridge, a dense cylinder of polypropylene fibers. Pleated cartridges fold the media like an accordion for more surface area, and many can be rinsed and reused. String-wound cartridges wrap yarn around a core. A spin-down filter uses a clear housing and a flushable screen, so you can rinse it without swapping a cartridge. Filters mount at one tap (point of use) or on the main line (point of entry).
What It Does Not Remove
A sediment filter only catches solids. It does not remove dissolved contaminants like nitrate, chlorine taste, heavy metals, or hardness minerals. For those you need other stages, such as an activated carbon filter for chemicals or a reverse osmosis membrane for dissolved solids. That is why the sediment filter comes first. It shields the carbon, the membrane, and a softener's resin from clogging grit, so they last longer. In dusty, hard-water Phoenix, that protection matters.