A sediment filter is the cheapest, simplest part of a whole-house water setup, and it’s the one people most often get wrong. The usual mistake is buying the finest cartridge on the shelf, which clogs fast and drags down water pressure. This guide covers what extension services recommend by water source, how spin-down screens and pleated cartridges differ, what the published pressure-drop numbers look like, and what replacement cartridges cost per year. Specs and prices come from official pages with the date we checked them, and our math is labeled as ours. We haven’t tested any of these filters.
The short answer
- Pick the micron rating by your water source, not “finer is better.” North Dakota State University Extension suggests about 15 microns for city water with rust, 10 to 15 for a drilled well, and 2 for a dug or bored well with fine clay (details below).
- If you can see sand or grit, go coarse first. A reusable spin-down screen or a coarse cartridge ahead of a finer one keeps the fine one from clogging in days.
- A sediment filter goes first. NDSU says it should be the first device after the water meter on city water, or right after the pressure tank on a well, ahead of a softener, carbon, or iron filter.
- Change it when the pressure drops, not by the calendar. A pair of pressure gauges (before and after the housing) tells you when.
- A sediment filter is for grit, not germs. It isn’t a disinfection device (see our UV guide for what is, and what it needs). If you’re on a well, get a coliform bacteria test from a state-certified lab and talk to your local health department about anything health-related.
What a micron rating means
A micron is one millionth of a meter, about 0.00004 inch, per the University of Massachusetts Extension fact sheet Microfiltration Treatment of Drinking Water Supplies (checked Oct 25, 2026). It explains the two ways filters are rated:
- Nominal: the filter catches most particles at the stated size. In UMass’s words, “some particles larger than the size rating will pass through, but how much larger and how many particles is not stated.”
- Absolute: “no particle larger than the stated size may pass through.” Those are used when a specific particle size matters.
Most whole-house sediment cartridges are sold with a nominal rating. The US Water Systems and Pentair cartridges below are all listed as nominal, so a “5 micron” nominal cartridge and a “5 micron” absolute cartridge aren’t the same thing.
UMass’s advice on picking a size is the key point of this whole guide: a smaller size “will require more frequent cleaning or replacement,” and “the largest rating size that will serve the purpose will require the least maintenance.”
Which micron rating for your water
NDSU Extension’s Filtration: Sediment, Activated Carbon, and Mixed Media (WQ1029, revised Feb 2022, checked Oct 25, 2026) gives these starting points:
| Water source | NDSU’s suggested rating |
|---|---|
| Public (city) water with rust or iron as sediment | about 15 microns “should be sufficient” |
| Private drilled well (larger particles plus fine iron) | 10 to 15 microns |
| Private dug or bored well (fine clay often present) | the finest available, 2 microns |
NDSU also says sediment cartridges come as woven string, pleated, or spun polypropylene, typically from 2 to 100 microns, and that a 2- to 5-micron filter “requires more pressure to push the water through.” It recommends a whole-house sediment filter for every house, city or well, and notes that activated-carbon filters “do not remove sediment or particulate material very well,” so carbon needs a sediment filter ahead of it.
US Water Systems makes the same point from the seller side on its sediment, sand, silt, and turbidity page (checked Oct 25, 2026): with large particles, “start with a 50 or 20 micron filter,” because “a 5 micron filter alone… would likely clog up very quickly.” It also admits sediment removal “is an inexact science,” so expect to try a size and adjust.
Our suggestion (a rule of thumb, not a standard): start at the coarse end of NDSU’s range for your water. If you still see grit in the toilet tank or faucet aerators, add a finer stage after it rather than replacing the coarse one with a finer one.
Spin-down screens vs cartridges
There are two common whole-house types for a home. (Self-cleaning backwashing media filters exist too, but they cost far more and need a drain.)
Spin-down screens are a clear bowl with a reusable mesh screen. You flush the sediment out by opening a valve at the bottom; there’s no cartridge to buy. They’re for sand and coarse grit, ahead of a finer filter. US Water Systems publishes a mesh-to-micron table on its 3/4-inch spin-down filter page (checked Oct 25, 2026):
| Screen mesh | Microns | Seller’s recommended use |
|---|---|---|
| 24 | 711 | Shale, sand, shell, or debris |
| 60 | 254 | Sprinklers and sand-sensitive valves; pipe scale and coarse sand |
| 100 | 152 | Fine sand and grit |
| 250 | 61 | Pre-treatment; very fine sand and grit |
| 500 | 30 | Pre-treatment; very fine sand and grit |
| 1000 | 15 | Pre-treatment for RO and ultrafiltration; ultra-fine sediment |
(That page lists more meshes; we’ve shown a selection.) Its specs: 3/4-inch FPT ports, 25 gpm maximum flow, 150 psi maximum at 73°F, but 100°F maximum at 40 psi, so it belongs on the cold line. Price on Oct 25, 2026: $71.95 for most screens, $74.95 for the 250, 500, and 1000 mesh screens (a “Halloween Sale” price). For 1-inch plumbing the Rusco 1-inch spin-down it sells is $92.50, or $95.75 with the finer screens, rated 1 to 25 gpm, with a two-year warranty (checked Oct 25, 2026).
Cartridge filters sit in a housing (the common whole-house size is 4.5 x 10 or 4.5 x 20 inches, often called “Big Blue”). They come in pleated, spun, or string-wound styles and get replaced when they clog. Pleated cartridges have more surface area, so they generally hold more dirt before the pressure drops. US Water Systems’ Magna pre-filter is one example (checked Oct 25, 2026):
- Housing with a pleated polyester cartridge, 0.5 to 20 micron options, 1-inch FNPT ports, 25 gpm peak flow, 90 psi maximum pressure. Price: $186.95 with a 5 or 20 micron cartridge, $196.30 with 1 or 0.5 micron.
- The seller says 1 to 3 bathrooms need the 10-inch size and 4 or more need the 20-inch.
- Seller claims we can’t verify: “up to 25 GPM with no drop in pressure,” 36 square feet of media in the 20-inch cartridge, and “12× more” dirt capacity than depth filters. Its cartridge page says it “conforms to NSF/ANSI 61 Certified by WQA”; we haven’t checked that in WQA’s listings, and NSF/ANSI 61 is a materials standard, not a performance claim.
- Replacement Magna 4.5 x 20 cartridges are $56.95 each for 5 micron (nominal, 25 gpm recommended flow). The seller notes they use an O-ring post seal and won’t fit a standard Big Blue housing, so you’re tied to its housings.
Pressure drop: what the published numbers show
Every filter costs a little water pressure, and a clogging one costs more. Few sellers publish numbers. Pentair publishes initial pressure drop (new, clean) for its Pentek parts:
- Housings (Big Blue spec sheet, checked Oct 25, 2026): a 20-inch Big Blue housing with 3/4-inch ports, about 2 psi at 15 gpm; with 1-inch ports, about 1 psi at 15 gpm. Maximum pressure is 90 psi for the 20-inch housing, and the temperature rating is 40 to 100°F. Pentair warns to protect it from freezing.
- Cartridge (R Series spec sheet, checked Oct 25, 2026): the R30-20BB pleated polyester cartridge (4.5 x 20 inch, 30 micron nominal), under 1 psi at 20 gpm when new. Pentair notes these figures are “based on manufacturer’s internal testing” and warns not to use them with “water that is microbiologically unsafe or of unknown quality without adequate disinfection.”
Our takeaway: a clean, coarse, full-size pleated cartridge in a housing with 1-inch ports should cost only a couple of psi at normal household flow, and 3/4-inch ports double the housing’s share. Finer cartridges and small 10-inch cartridges cost more, and the drop grows as the cartridge loads up.
How to know when to change it: UMass says that as a filter clogs, “the pressure drop across the filter increases and water flow decreases,” and that’s the signal for service. Put a pressure gauge on each side of the housing, write down the difference when the cartridge is new, and change it when that difference climbs noticeably or the shower weakens. A clear housing also lets you see it filling up.
What cartridges cost per year (our math)
Using the Magna 4.5 x 20, 5 micron cartridge at $56.95 (checked Oct 25, 2026), and the seller’s own FAQ answer that “a common guideline is about 3–6 months” (it also says there’s “no fixed lifespan”):
| Change interval | Cartridges per year | Cartridge cost per year |
|---|---|---|
| Every 6 months | 2 | about $114 |
| Every 4 months | 3 | about $171 |
| Every 3 months | 4 | about $228 |
That’s our multiplication; your sediment load sets the real interval. Dirty well water can clog a fine cartridge in weeks, which is exactly when a reusable spin-down screen ahead of it starts paying for itself. A $72 spin-down that doubles cartridge life would save about $57 to $114 a year at these prices (our math, assuming it actually doubles the life, which depends on how much of your sediment is coarse).
Where it goes in the line
- City water: after the water meter, ahead of a carbon filter or salt-free conditioner (NDSU). Our chloramine and whole-house carbon guide covers the carbon step.
- Well water: right after the pressure tank (NDSU), ahead of an iron filter or softener. See Iron and Manganese in Well Water for when you need an iron filter, which a sediment cartridge can’t replace. NDSU describes oxidizing filters as turning dissolved iron and manganese into particles that the filter then traps; a plain sediment cartridge doesn’t do that first step.
- Ahead of a softener: a sediment filter doesn’t change softener sizing; size on hardness with our softener sizing calculator. US Water Systems’ own installation guide recommends a sediment pre-filter ahead of carbon or softening media to prevent clogging.
- Add a bypass and leave room under the housing to remove the bowl, and keep it out of anywhere that can freeze. Where the filter sits relative to a softener and the water heater is covered in our softener installation checklist.
Certifications
NSF/ANSI 42 includes a “Nominal Particulate Reduction” claim with classes from Class I (finest) to Class VI (coarsest). In our full read of NSF’s NSF/ANSI 42 listings on Oct 21, 2026, some point-of-entry systems carried that claim (we saw Classes I, III, and V). A micron number on a box or product page is the seller’s rating, not an NSF claim, so match the exact model number in NSF’s listing before relying on one. NSF’s site was unreachable from our tools on Oct 25, 2026, so we couldn’t re-check. NSF lists no US Water Systems softener system, only some filter-cartridge components with “material requirements only” (our Oct 20, 2026 read). For how to look a product up yourself, see NSF/ANSI certifications explained.
Checklist
- Know your water: read your utility’s Consumer Confidence Report, or for a well, get a state-certified lab test (include coliform bacteria and iron). See how to find your water hardness.
- Pick a starting micron rating from NDSU’s table for your source, at the coarse end.
- Visible sand? Put a spin-down screen ahead of the cartridge, picking the mesh from the seller’s table for the kind of grit you see.
- Choose a housing with ports that match your plumbing (1-inch costs less pressure than 3/4-inch), and check its pressure and temperature limits.
- Install gauges before and after, and change or clean when the difference rises.
- Keep a log of change dates, as UMass recommends, so you learn your real interval.
A sediment filter protects plumbing, fixtures, and the equipment after it. It doesn’t make water safe to drink; for health questions, start with your local health department.