Sediment Filter Types: Which One Does Your Water Need?

A sediment filter is a physical sieve. Water passes through a porous cartridge and anything larger than its pore size is trapped: sand, silt, clay, rust particles, pipe scale. That is all it does.

It removes nothing dissolved. TDS, hardness, fluoride, arsenic, pesticides, bacteria and viruses all pass straight through. That is why every purifier puts a sediment stage first and something else — RO, UV, UF or carbon — after it. The sediment stage's job is to protect those later stages from clogging.

The micron rating is the approximate particle size the filter stops. Smaller numbers stop finer particles, but they also clog faster and cut flow sooner.

• Spun (melt-blown) polypropylene — the white cylinder in almost every Indian purifier. Cheap, consistent and food-safe. It is a depth filter, trapping particles through its thickness. Not washable; replace it.
• Pleated — a folded sheet with far more surface area. Holds more dirt before flow drops and can usually be rinsed and reused a few times. Better for high-sediment water; costs more upfront.
• String-wound — polypropylene or cotton yarn wound around a core. Handles heavy sediment and rust well, which makes it a common choice for iron-rich borewell water.
• Backwashable / spin-down — a reusable mesh screen (often 50–100 micron) with a flush valve. No cartridges to buy; used as whole-house protection at the tank inlet, not for drinking-water polishing.

• Municipal supply, water looks clear — you need nothing extra. The 5-micron cartridge inside your purifier is enough.
• Tanker water, or occasional muddy supply — add an external 20-micron spun or pleated pre-filter before the purifier.
• Borewell water with rust or iron staining — a string-wound pre-filter, plus an iron-removal stage if the staining is heavy. A sediment filter traps rust particles but not dissolved iron.
• Whole house (bathrooms, washing machine, geyser) — a backwashable 50–100 micron filter at the overhead-tank outlet.

There is no fixed interval — it depends entirely on how dirty the water is. The two reliable signs are a drop in flow from the purifier and a cartridge that has turned brown or orange. On clean municipal water a spun cartridge can last 6–12 months; on borewell or tanker water, 2–4 months is common.

A clogged sediment filter does not make water unsafe, but it starves the RO membrane of pressure, which cuts output and raises the reject-water ratio. Replacing a ₹150–₹300 pre-filter on time is the single cheapest way to protect a membrane that costs several thousand rupees.