Pure Water Occasional

Special Mid-Month Issue

March 15, 2012

Read This Issue on the Pure Water Occasional Website

Water Filter Cartridges


One of the great advances in modern water treatment is the increased availability of excellent replaceable water filter cartridges. Not only are there more cartridges available to deal with an increasing number of water issues, but the old standbys like carbon and sediment cartridges have been greatly improved in recent years.

Replaceable cartridges contribute variety to water filtration equipment, allowing the same device to be used for a number of purposes. And multi-canister systems can be made to perform multiple tasks.

From the seller's viewpoint, replaceable cartridges are the razor blades of the water treatment industry. A satisfied customer with an excellently performing water treatment unit replaces filter cartridges year after year. The periodic replacement of cartridges keeps the dealer in touch with the customer and encourages ongoing upkeep of the treatment unit. This benefits both the dealer and the customer.

The Pure Water Occasional's Concise Guide to Water Filter Cartridges

The advantages of using replaceable cartridges in water filters are numerous. These include:

1. Convenience and ease of maintenance.

2. The versatility that comes from being able to use a single filter style for many purposes.

3. Easy renewal of the filtration unit to optimal performance. (When you put a new cartridge in a water filter, it performs like a new water filter.)

Classifying Filter Cartridges by Design

Water filter cartridges fall into two broad design categories--radial and axial. With radial cartridges, which have a permeable outer wall, water flows through the outer wall of the cartridge into the center. With axial cartridges, which have a hard, impermeable outer wall, water enters one end of the cartridge, flows through the length of the cartridge, and exits the other end.

Axial Cartridge. Water flows from one end to the other. Granular "media" filters are made in this format.

Radial Cartridge. Water flows from outside to the inner core. All carbon block and sediment filters fall into this category.





Classifying Filter Cartridges by Size


Cartridge Group 450

Above is an introductory cartridge selection image from our recently revised cartridge page. (The website image has mouseover identifications and links to the sections represented by the cartridges. Click the link above and try it out.)

Larger Image.

For some years, we've had an "in house" size classification system for cartridges. Now I'm going to share it with the world.

We divide standard filter cartridges into four basic sizes:

Size 1: 9.75" X 2.5". Size 1 cartridges are often referred to in the industry as "ten-inch cartridges." The length measurement is fixed, but the diameter can vary some. If the cartridge measures 9 3/4" X 2 1/4", it's still a Size 1 cartridge. This is the most common filter cartridge size. Almost everyone who makes a water filter makes cartridges in this size. We consider this a drinking water filter size, although discount stores sometimes offer "whole house" filters in this format as well.

Size: 2. 20" X 2.5". This popular size is the same diameter as size one but has double the length. It's a common "whole house" sediment and light-duty carbon size.

Size 3: 10" X 4.25". This is the size that's often referred to as "Big Blue," because the original maker of the housing made them only in blue. Size 3 supports a bit more flow capacity than Size 2, and it is a favorite as a "whole house" sediment filter or a light duty whole house carbon. As with Size 4 below, Size 3 cartridges vary in diameter and often are 4.5".

Size 4: 20" X 4.25". This size, which we also call "double Big Blue," is a full flow size that works well for whole house sediment, carbon, and media filters.

There are other standard sizes that we don't list because there is so little demand for them. For example, if you want a 2.5" X 40" sediment filter, call and we can get it for you in a couple of days.

Other cartridge sizes that we list on the cartridge page of our main website are classified variously. These are mainly proprietary cartridges. (In water treatment jargon, proprietary means that the maker has purposely created an unusual size so the customer will have to return to the manufacturer for replacements.) Here are the main categories from our web page.


General Category Description Comment
Sprite Shower Filters Sprite High Output and Hand-held. We currently stock only the two most popular Sprite proprietary cartridges, but more are on the way.
Candle Cartridges These are "Doulton Candle" screw-in cartridges, plus the generic carbon blocks and sediment that fit our Slimline Model 77 countertop. Doulton also makes cartridges in the standard Size 1 style.
Microline and Hydrotech Proprietary carbon blocks and sediment for Microline and Hydrotech filters and RO units. Microline and Hydrotech RO membranes are also offered.
Omnipure Q Series 12" Q Series for our Q Series RO units and filters. Proprietary cartridges. We have granular coconut shell carbon, sediment, carbon blocks, DI, and phosphate cartridges in this format.
Multi-Pure Multi-Pure is a proprietary brand. We stock VOC (commercial) plus the popular MLM sizes, mainly as a convenience to customers. Drinking water filters only. We don't stock Multi-Pure's fringe products.
In-Line Filters Popular sizes (mainly 10" and 6") GAC, carbon blocks, polyphosphate, GAC/KDF, and sediment. These are disposable filters, frequently used as RO postfilters and refrigerator filters. We don't always make a brand distinction for inlines. We consider premium brands (Omnipure, Pentek) as interchangeable. We don't stock quick connects in all sizes, but we can add quick connect fittings to a standard threaded inline if you ask.
RO Membranes All popular residential sizes, mainly in Filmtec, Watts, and GE brands. We also stock one GE encapsulated membrane to support our Q Series RO units. We stock large membranes for our Watts R12 RO units as well. We know that membranes aren't, technically, filter cartridges, but for reasons of convenience we list them as such.


Classifying Filter Cartridges by Function

Cartridge Types

Carbon Block: For reduction of chlorine, chloramine, chemicals, plus taste/odor improvement. Some carbon blocks are enhanced with added lead reduction resins. We stock both standard carbon and coconut shell carbon blocks.

Granular Carbon: For reduction of chlorine, chloramine, chemicals, plus taste/odor improvement. Some granular carbons are enhanced with added KDF for extended performance and metals reduction. Both standard and coconut shell carbons are offered.

Media. "Media" cartridges are granular specialty filters for iron, fluoride, nitrates, arsenic, hydrogen sulfide, low pH, hardness, and more.

Sediment: Sediment filters in three basic formats remove particulate.

Ceramic: Reduction of cysts, bacteria, and viruses.

Using our Cartridge Pages

We've completely redone our main filter cartridge page. Cartridges are clearly arranged by type and size, and each cartridge now has a picture and a listing of essentials. Where applicable, links are provided to the manufacturer's technical literature. Here, for example, is a media cartridge from the Size 1 section.

Nitrate Removal Cartridge

part# fc010

FloPro High Quality Nitrate Reduction Cartridge.

Can be regenerated to some degree with salt water. It contains high capacity nitrate selective anion exchange resin. A cartridge this size will typically remove 7500 ppm/ gallons (meaning, for example, if you have 10 parts per million nitrates in your water, you should change or regenerate it at about 750 gallons). Performance can vary considerably according to flow rate and other water constituents.

Fits any standard housing made for 2.5" x 9.75" cartridges.

Recommended for:

  • Nitrate Removal

Cartridge Details

manufacturer: FlowPro
manufacturer's part# FPNSR-975
media: Anion Resin
cartridge capacity: 4,000 grains @ 0.5 gpm
flow direction: Axial
Nitrate Cartridge

In addition to the regular cartridge page that presents products by size and type, we also offer a second page that features listing by part number. This is for the convenience of those seeking to reorder cartridges whose part numbers they know. Our customers receive post card reminders when their filter cartridges are due for replacement, and the reminder lists the part number. This system makes cartridge reorders very easy.

The Refillable Cartridge--A Little Known Resource

If you are a large consumer of filter cartridges, here are a couple of ideas that might help.

Pleated sediment cartridges, five microns or larger, are to some degree cleanable and reusable. Although they cost a bit more, getting several uses from the cartridge can save a lot.

With media cartridges for such purposes as softening, deionization, fluoride reduction, and nitrate reduction, you can purchase refillable cartridge shells ($4 to $14 in the the four standard sizes listed above) and fill them yourself with bulk media. Here' s B. B. Sharper's breakdown of cost for a couple of sample situations where customers might want less expensive replacements.


Price of a refillable Size 1 cartridge--$4.

Price of a "ready-made" water softening cartridge -- $19

Price of one cubic foot of softening resin -- $109

Number of "refills" for a Size 1 refillable cartridge in a cubic foot of media -- 40.

Cost per cartridge if you purchase a cubic foot of softening resin and a refillable cartridge --$2.83

Price of one "ready-made" Size 1 deionizing cartridge -- $29

Price of one cubic foot of mixed bed DI resin -- $368

Cost per DI cartridge if you purchase a cubic foot of resin and make your own -- $9.30.

Approximate number of Size 1 cartridges that can be filled with one cubic foot of media--40.

Approximate number of Size 2 cartridges that can be filled with one cubic foot of media--l7

Approximate number of Size 3 cartridges that can be filled with one cubic foot of media--16

Approximate number of Size 4 cartridges that can be filled with one cubic foot of media-- 7

Common Sense About Cartridges

Filter cartridges aren't magic. They follow the rules of the physical universe and are, consequently, limited. While many cartridges can perform amazing amounts of work, others are by nature only short-term performers.

A top Size 1 carbon block cartridge, for example, can remove chlorine from literally thousands of gallons of city tap water. The same cartridge can also protect against chlorination by- products for up to a thousand gallons. This is an impressive performance, and you get a lot for your money.

A water softening cartridge, by contrast, may only work for a few gallons if used for washing a car with hard tap water. To expect it to provide a summer's worth of car washes is unreasonable. (For details.) The same cartridge, if used to polish off the ammonia left behind by an RO membrane can last for hundreds of gallons.

The moral is learn something about the cartridge and its capacity before you buy. Don't buy and expect miracles based on the name of the cartridge alone. We stopped selling sodium reduction cartridges because customers expected too much of them.

We really hope you'll look at our new cartridge page on our main website.

The Pure Water Occasional is a project of Pure Water Products. Please visit our websites:

Main Website: www.purewaterproducts.com. This site features our full range of products, plus instructions, technical articles, product manuals, and more.

The Occasional's Website: www.purewateroccasional.net. In addition to archiving back issues of the email Occasional, this site houses a sizeable section about water contaminants, a "how things work," series, a new products section, a glossary of water treatment terms, and, "much, much more."

Other Pure Water Products Sites:


Write Us.

To contact us by phone, please call 940 382 3814.