A sediment tank is a media-filled vessel with an automatic control valve on top that strains grit, sand and silt out of the incoming water and then flushes the accumulated dirt to a drain on a schedule. It does the same job as a cartridge filter, but it holds far more dirt and cleans itself instead of needing a cartridge swapped, which is why heavy sediment loads on well systems usually end up in a tank.
How a backwashing tank differs from a cartridge
A cartridge housing traps sediment in a disposable element that fills up, restricts flow and gets thrown away. A sediment tank holds a graded bed, often layered sand and garnet or a lightweight granular medium, and traps particles through the depth of that bed rather than on a single surface. When the control valve triggers a backwash it reverses the flow, lifts and fluidizes the bed, and carries the trapped dirt out to the drain, after which the bed resettles by particle size and goes back to work. Nothing is consumed except water, which is the whole appeal on a well that would otherwise eat a cartridge a week.
When the tank is the right call
Go to a tank when the sediment load is heavy, when the flow demand is high enough that cartridge housings cause a real pressure drop, or when the filter is somewhere inconvenient to service regularly. A well recovering from a new pump installation, a shallow well that stirs up after rain, or a supply carrying fine sand from the formation all qualify. Stay with cartridges when the water is mostly clean and you only want polishing, when there is no drain within reach, or when there is no floor space for a tank plus the clearance above it that media changes need. City supplies rarely justify a sediment tank.
Micron rating, and its limits in a tank
Cartridges advertise a micron rating and tanks generally do not, because a graded bed does not have a single pore size. What a tank gives you instead is depth: fine particles are captured through the bed rather than at one plane, so the tank keeps working long after a cartridge of similar nominal rating would have blinded. The tradeoff is that a tank is less precise at the fine end. Where genuinely fine filtration matters, such as ahead of a reverse osmosis membrane or a UV lamp that needs clear water to work, the usual build is a tank for the bulk load followed by a cartridge for the polish.
What the installation and the drain need
The tank goes right after the pressure tank on a well or after the main shutoff on a city line, upstream of everything else, with a bypass loop so the house can keep water while the unit is serviced. Backwash needs a drain that can take the full backwash flow, with an air gap so nothing can siphon back into the treated water, and on a septic system that flush volume has to be somewhere the drain field can accept. Power is needed for the valve. Our best sediment filter for well water guide covers matching bed size to the flow the household actually draws rather than to pipe diameter.
Questions people ask about sediment tank
Does a sediment tank need cartridges?
No. It backwashes the trapped dirt to a drain instead, so the running consumable is water rather than a replacement element.
How often does a sediment tank backwash?
The valve is programmed for it, commonly every night or every few days depending on load. Heavy sediment justifies a more frequent cycle.
Can I put a sediment tank on a septic system?
Often yes, but the backwash volume has to be somewhere the drain field can handle. Check local rules and the capacity of your system first.
Do I still need a cartridge filter after a tank?
If a membrane or UV lamp is downstream, yes. A cartridge polishes the fine particles the graded bed lets through and protects the sensitive stage.