Sediment Filter Micron Rating: 5 vs 20 (and Up)

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Quick answer from a licensed plumber: Lower is finer: a 5-micron cartridge stops finer particles than a 20-micron one, but it clogs sooner. On city water a single 5-micron sediment cartridge is the common choice. On sandy well water, put a coarse 20 to 50 micron stage first and a 5-micron stage after it. The Pentair sediment cartridges on this page are rated nominal, which is not a guaranteed cut-off; only an absolute rating carries one (Pentair defines it as 99.98% at the stated size).

Standard 10″ housing on city water? A nominal 5-micron cartridge like the Pentek P5 is the usual pick. See the Pentek P5 on Amazon

Micron Ratings at a Glance

A micron is a millionth of a meter, and a lower number means a finer filter. What the number does not tell you is how much of that size the cartridge catches, which is the nominal-versus-absolute question below. Here is what one maker, Pentair, actually sells at each common rating in its Pentek and American Plumber lines:

Every rating in this table is a nominal rating; Pentair’s American Plumber sheet says so outright (“Micron ratings are nominal”), and its Pentek P, R and DGD sheets label their rating columns nominal.

Nominal vs Absolute: Why “5 Micron” Is Not a Guarantee

Pentair’s industrial filter catalog defines an absolute rating precisely: “Absolute defined as Bx >5,000 (99.98% efficiency at stated micron size).” It sells absolute and nominal versions of the same cartridge families under different prefixes.

A nominal rating has no such number on Pentair’s residential sheets. We checked the P, R, DGD and American Plumber sheets and none of them prints a capture percentage for nominal. So treat a nominal 5-micron cartridge as “built to stop most particles around 5 microns,” not “stops everything 5 microns and up,” and compare nominal to nominal. If a job truly needs a guaranteed cut-off, that is an absolute-rated cartridge and usually a different, more specialized product.

5 Micron or 20 Micron?

Finer catches more, but it also fills faster, and a clogged cartridge shows up as low pressure at every tap. Pick by what is in the water:

• City water with little visible sediment: a single 5-micron cartridge is the common choice. Pentair’s W20CLA pleated cellulose (20 micron) is also built for this; Pentair says it is “designed for municipal/chlorinated water (not recommended for well water applications).”
• Well water, or sand you can see in the sump: start coarse. Pentair’s American Plumber sheet calls its 30 and 50 micron pleated polyester cartridges “excellent for well water applications,” and the Amazon listing for the Pentek R30-20BB says it works with city or well water. Then add a 5-micron stage after it.
• Before a carbon cartridge or a reverse osmosis unit: put a sediment stage first so grit does not load the carbon. Pentair’s RFC carbon cartridges have a 70-micron outer shell, which is a screen for the carbon bed, not a sediment filter.

Staging: Coarse First, Fine Second

When sediment is heavy, two stages outlast one fine cartridge doing all the work. Pentair builds this idea into a single cartridge too: its DGD series “combines selective final filtration with appropriate pre-filtration to achieve up to three times the dirt holding capacity of similar size sediment cartridges.” In a two-housing setup the usual order is the coarser cartridge (for example a 30-micron R30) on the inlet side and the finer 5-micron cartridge after it.

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Spun, Pleated or String Wound?

• Spun polypropylene (P series): Pentair says the fibers form “a true gradient density from outer to inner surfaces,” so coarse particles stop near the outside and fine ones deeper in.
• Pleated polyester (R series): more surface area; Pentair says the standard 9.75-inch R cartridge has “more than four square feet” of fabric and the Big Blue version “more than 16 square feet.” Pentair calls the media reusable, but its American Plumber sheet adds: “Reuse not recommended for potable water applications.” For drinking water, replace it.
• Pleated cellulose (W5CP, W20CLA): Pentair designs these for municipal/chlorinated water and does not recommend them for wells.
• String wound (W5W, W30W, W50W): Pentair’s American Plumber sheet describes its polypropylene string wound cartridges as “ideal for well water applications.”

Match the Size Before the Micron

The micron rating only matters once the cartridge fits. Check the length (10 or 20 inch) and the diameter (the 2.5-inch class or 4.5-inch Big Blue) of the old cartridge, and buy the same size in the rating you want (our cartridge size chart shows how to measure). Pentair also notes that the same cartridge is rated for different flow in different housings: its American Plumber chart gives the W5P 5 gpm in a 3/8″ Slim Line housing and 10 gpm in a 3/4″ Standard housing.

What to Buy

Pentair Pentek cartridges in the ratings above, all shipped and sold by Amazon when we checked:

• 5 micron, 10″ x 2.5″: Pentek P5.
• 1 micron, 10″ x 2.5″ (final stage): Pentek P1.
• 30 micron pleated, 10″ x 2.5″ (coarse first stage): Pentek R30, or Pentek R50 at 50 micron for heavier sand.
• Big Blue 20″ x 4.5″: Pentek R30-20BB (30 micron) as the first stage and Pentek DGD-5005-20 (5 micron) as the second.

Parts You’ll Also Need

For the cartridge change itself:

• Food-grade silicone grease for the housing O-ring: Captain O-Ring NSF food-grade silicone grease. Pentair’s Slim Line housing sheet says to lubricate the O-ring with food-grade silicone before the sump goes back on.

When to Call a Licensed Plumber

• Cartridges clog within days. That usually means heavy sediment from the well or the street main, and the fix may be upstream of the filter. On a well, a reusable spin-down ahead of the cartridge is the usual fix; see sediment filters for well water.
• You want to add a second housing for staging; that means cutting into the line.
• Your pressure drops at every fixture even with a fresh cartridge.

FAQ

Is 5 micron or 20 micron better for a whole-house filter?

Five micron catches finer particles but fills faster. For city water with little sediment, a 5-micron cartridge is the common choice. For sandy well water, start with a coarser 20 to 50 micron stage and add a 5-micron stage after it.

What is the difference between nominal and absolute micron ratings?

Pentair’s industrial catalog defines absolute as Beta greater than 5,000, or 99.98 percent efficiency at the stated micron size. The Pentek and American Plumber sediment cartridges on this page are rated nominal, and those sheets print no capture percentage, so a nominal rating is not a guaranteed cut-off.

Can I reuse a pleated sediment filter?

Pentair calls its R Series pleated polyester reusable, but its American Plumber sheet says reuse is not recommended for potable water applications. For drinking water, replace the cartridge.

Does a 1 micron sediment filter make well water safe?

No. Pentair warns not to use its sediment cartridges with water that is microbiologically unsafe or of unknown quality without adequate disinfection. Have the well tested and treat it for bacteria separately.

Which comes first, the sediment filter or the carbon filter?

Sediment first. A sediment stage keeps grit from loading the carbon. Pentair’s RFC carbon cartridges have only a 70-micron outer shell, which is not meant to do the sediment filter’s job.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. Every part number, size and fit on this page comes from the manufacturer pages and documents listed below, which we opened and read; product details come from those makers and from the Amazon listings, not from hands-on testing. Each linked product was shipped or sold by Amazon, new and in stock, when we checked on September 24, 2026. Nobody pays to be included here. Where a link goes to Amazon we may earn a commission at no extra cost to you. More on who writes this and how we pick.

Sources

• Pentair: Pentek P Series cartridge spec sheet (310060)
• Pentair: Pentek R Series cartridge spec sheet (310066)
• Pentair: Pentek DGD Series cartridge spec sheet (310061)
• Pentair: Pentek RFC Series cartridge spec sheet (310075)
• Pentair American Plumber: sediment cartridges sheet (300026)
• Pentair Engineered Filtration: filter cartridge catalog
• Pentair: Pentek Traditional Slim Line housing spec sheet (310050)

Bottom Line

Choose the micron by what is in your water, and stage coarse to fine if there is a lot of it. Compare nominal ratings with nominal ones, remember a sediment cartridge does not disinfect, and get the size right before you worry about the number.