Big Blue Water Filter: Complete Guide to 10" and 20" Housings

A Big Blue is a 4.5 inch diameter cartridge filter housing, Pentair's name for its Pentek heavy duty line. It comes 10 or 20 inches long, takes a 5 micron cartridge, and hangs on the wall right after your well tank to catch the sediment before it reaches anything you paid real money for. I recommend the 20 inch for most homes; for one or two people, the 10 inch does the job.

Caller "When I looked it up, it said to do the Big Blue filter first, and then..."

Aidan "Yeah, you always wanna put a Big Blue filter first before any type of equipment, to try to keep the sediment out of the tank and keep the valve clean."

A caller in June, putting an arsenic tank on a rental's well. This page is the long version of that answer.

What a Big Blue filter is

"Big Blue" is the maker's name for this housing: a blue bowl 4.5 inches across and 10 or 20 inches long, called the sump, under a black cap the pipes screw into. The maker is Pentair, under its Pentek brand, and the cap comes with 3/4, 1 or 1-1/2 inch pipe ports. The ones in our kits are the 1 inch port models, Pentek 150237 for the 10 inch and 150233 for the 20 inch, each with the red pressure relief button on the cap. Pentair's own spec sheet has them tested to NSF/ANSI 42 for materials and structure, rated for 40 to 100 degree water, and built for the cold line only. The sump has to be kept from freezing.

The housing does no filtering by itself. Water comes in the cap, goes down the outside of the cartridge, through it to the center, and back up out the cap. Whatever the cartridge is rated for is what the Big Blue is rated for. Our kits ship with a 5 micron cartridge, and 5 micron is the only rating I put in one; more on that below. The housing takes any 4.5 inch cartridge of the right length, Pentek's or another maker's; Pentair says so on the 150233 page.

The reason a 4.5 inch housing instead of the skinny 2.5 inch ones: flow. Pentek rates both of our housings at a 1 psi drop at 15 gallons a minute with nothing in them, and Pentek's own 20 inch 5 micron cartridge drops less than 1 psi at 20 gallons a minute on its sheet. A whole house runs through it and nobody in the shower knows it is there. That is what I meant on camera by "it doesn't slow down your water pressure or cause a big pressure drop."

One more thing the name covers. A Big Blue housing with a carbon cartridge in it is a different product for a different job (chlorine, taste, odor), and it goes after the treatment tanks, not ahead of them. If that is what you are after, those are with the whole house carbon filters. Everything on this page is about the sediment housing.

10 inch or 20 inch Big Blue

I recommend the 20 inch for most homes because it gives you greater capacity without a pressure drop; if you are just one or two people living in the house, you can get away with the 10 inch. Same diameter, same cap, same 1 inch ports. The difference is 10 inches of sump and 10 inches of cartridge, and that is the difference between changing the cartridge and changing it twice as often.

The $30 between them buys twice the cartridge. Same sediment, same water, and the 20 inch cartridge has twice the media to load up before the flow starts to fall off. Pentair sizes the 20 inch housing for a household of 4 or more; a contractor called me in September about a two-person home on a pH 6 well, and I still told him a 20 inch 5 micron kit ahead of the neutralizer. If the wall has the room, the 20 inch is the one.

The 10 inch earns its place two ways: one or two people with light sediment, or a spot where 23 inches of housing plus the room to drop the sump will not fit. For a bigger house with a lot of sediment, size is not the fix; the fix is a different kind of filter, and that decision is on the page about cartridge vs spin-down vs backwashing tank. Sizing by pump and flow rate is on the page about sizing a sediment filter by pump, flow and sediment kind.

Where the Big Blue filter gets installed

It mounts to the wall next to your well tank, right after the well tank and before your first water treatment system. Every filter goes after the tank; nothing goes between the pump and the tank. If you are putting in an acid neutralizer, an iron filter or a softener, the Big Blue goes in first, the water passes through the 5 micron cartridge, and then it goes to the tank.

A woman called me in September about a 26-year-old well, pH 6.3, hard water. Her plan came out in one sentence: "twenty-inch Big Blue sediment filter before the neutralizer. So you would go sediment filter, neutralizer, water softener, UV light if you went that way." She remembered sediment in the toilets when the well was new and not much now, and asked whether she still needed it. If you don't put one in, over time you get build up in the bottom of the neutralizer tank, because it is first in line. It restricts the flow until you notice it, and then you have to take the tank outside and dump it, and it weighs three hundred and some pounds full of wet calcite and water. So I'd definitely put that first.

The Rusco spin-down screen is the other filter people ask about, and it goes at the other end: last, after the treatment tanks, to catch grit and media they let past. It is a coarse screen, 60 mesh on the ones we sell, which is about 250 microns, so it is not a substitute for the 5 micron cartridge up front. How that filter works is on the page about the spin-down type, and the full order of every piece of equipment is on the page about how sediment filters work and where they go in the line.

Not sure which size you need

Send me a photo of your tank area

Tell me how many people are in the house and what tanks you have or are adding. I will tell you 10 inch or 20 inch and where on the line it goes.

Text Aidan443-277-2204 Call800-460-5810Aidan

8 AM to 5 PM Eastern, seven days a week. A real person, not a call center.

What comes in the Big Blue kit

What ships: the housing with its red pressure relief button, the wall bracket, the wrench that fits the sump, and the 5 micron cartridge already in the housing. Pipe fittings, shut-off valves and Teflon tape are not included; your plumber brings those to match your pipe.

It has a bracket and mounts to the wall. The housing full of water is heavy enough that the bracket goes on a stud, block or solid backing, and it hangs with the sump straight down so the sump can be unscrewed for a cartridge change. Leave room under it for that.

We recommend installation by a licensed plumber; I support your plumber by phone at 800-460-5810. On video I put a filter like this one, with no drain line and no electricity to run, at one or two hours for a plumber who knows what he is doing. The steps, the fittings list and the Rusco install are on the page about how to install a sediment filter.

The cartridge inside the Big Blue

Every Big Blue kit we sell ships with a 5 micron cartridge, and 5 micron is the only rating I put in one. As I told a caller in March, "we use the polyspun five-micron cartridges in our Big Blues. We don't use any other size filter." Five microns is far smaller than a human hair (about 70 microns) and finer than the eye can see, and it takes out the sand, silt, rust and clay that a coarser cartridge lets through. Callers tell me "I have a 25 micron filter, but I still get dirt passing through." Same housing; swap in a 5.

The cartridge that ships in each kit is a melt-blown polypropylene 5 micron, what the trade calls polyspun: a cartridge spun from fibers rather than wound from string. Pentek's own melt-blown line, the DGD, is spun so the fibers get denser from the outside in, and Pentek says it holds up to three times the dirt of a similar-size sediment cartridge and more than a standard spun or string-wound one. The 10 inch replacement we sell, the Pentek WP5BB97P, is the other common construction, polypropylene string wound around a core; Pentek rates it 5 micron nominal with less than a 3 psi drop at 20 gallons a minute. Both do the job. Pleated cartridges also fit the housing; we do not sell them.

	Cartridge	Which Big Blue it fits	Price
	The cartridge in the 10 inch kit: 5 micron, 9 3/4 inches long	The 10 inch Big Blue	Included in the $165 kit
	The cartridge in the 20 inch kit: 5 micron, 20 inches long	The 20 inch Big Blue	Included in the $195 kit
	10 inch replacement: 5 micron, 9 3/4 inches long (Pentek WP5BB97P)	Fits any 10 inch Big Blue	$45
	20 inch replacement: 5 micron, 20 inches long	Fits any 20 inch Big Blue	$55

You do not have to buy the replacement from me. A 5 micron cartridge will on average cost you about $25 if you get it locally; most plumbing supply houses carry them, and sometimes Lowe's, Home Depot or Walmart. Just match the length to your housing: 9 3/4 inch for the 10 inch Big Blue, 20 inch for the 20 inch, 4.5 inches across either way. If the store only has a 20 or 25 micron, it will fit and it will let dirt through. Which rating does what is on the page about which micron rating.

When to change the Big Blue cartridge

Every 4 to 6 months or so you are going to replace the cartridge inside; it depends on how much sediment you have in the water, so it could be every 12 months, it could be every other month. Pentek's own instructions give you the sign: a decrease in water flow means the cartridge should be replaced. When the shower or the washer starts filling slower than it did, the cartridge is loaded.

The other check costs nothing. Go in the bathroom you use most, take the lid off the toilet tank, and look. Dirt and sediment in there means it is getting past whatever you have. Callers ask whether they can wash the cartridge off and reuse it; you can do whatever you want to, but I recommend you replace the cartridge when it becomes dirty. It is a $25 to $55 part protecting tanks that cost $1,000 and up. The change itself, from Pentek's instructions:

1. Turn the water off first

   Close the shut-off ahead of the housing (and the one after it, if you have a bypass). Press the red pressure relief button on top of the cap and hold it until the hissing stops. If shutting the filter off shuts the house off, fill a bucket first for rinsing the sump.

   

2. Unscrew the blue bowl with the wrench

   Fit the spanner wrench from the kit around the sump and turn it off the cap. A bucket under it catches what is left in the housing. Lift the old cartridge off the standpipe and throw it out.

3. Grease the rubber O-ring

   Lift out the large O-ring, wipe it clean, and set it aside. Rinse the sump, scrub it with a nonabrasive sponge, and rinse again. Put a thin coat of clean silicone grease on the O-ring, clean its groove, and press it back into the groove with a finger so it sits flat all the way around. A pinched O-ring is where a Big Blue leaks.

4. Drop in the new 5 micron cartridge

   Set the new cartridge over the standpipe in the bottom of the sump. Screw the sump back onto the cap and hand-tighten only; Pentek says do not over-tighten. Make sure the cap's standpipe slips into the top of the cartridge as it goes up.

   

5. Fill the filter back up slowly

   Open the shut-off slowly so the housing fills, then press the red button again to let the trapped air out. Open a faucet and run it about 5 minutes to flush the new cartridge. Check the sump for drips before you walk away.

One line item most people never hear: Pentek says the plastic sump itself has a service life and should be replaced at ten years for the opaque blue sump. Write the install date on it.

What a Big Blue does not remove

A sediment cartridge catches dirt, sand, silt, rust and clay; it does not remove anything dissolved in the water. That means no dissolved iron or manganese, no hardness, no low pH, no chlorine taste and no bacteria. A man called me in June with brown water, a rotten egg smell, and a three-housing cartridge rack he had bought to fix it. He had pulled his pre-filters and found them "muddy-looking." That is iron with red clay in the water. His cartridges had caught the clay and let the iron straight through, because the iron was dissolved, and cartridges "don't work" on that. What he needed was a Katalox iron tank, with a 4 by 20 Big Blue ahead of it to catch the clay so the tank did not have to.

So the Big Blue is the first stage, not the treatment. Dissolved iron and sulfur are the iron and sulfur filters. Low pH is the acid neutralizers. Hardness is the water softeners. Bacteria is a UV light, after the cartridge, not instead of it. The Big Blue's job is to keep sand and clay out of the valves and media in all of those. The Rusco screens and the backwashing tank for heavy loads are with the sediment filters.

Frequently asked questions