Issue: 8/05

Anyone familiar with cartridge filters will know that they come in a bewildering variety of types and sizes. Their relatively low capital equipment costs, ability to handle varied service flows, and minimal space requirements make them an attractive method of solving water problems.

Cartridges hold many advantages. For starters, they can be plumbed in-line to give relief to a specific problem, without the need for backwashing or waste flow handling. Maintenance becomes a periodic change-out of the cartridge per the manufacturer's prescribed frequency-an easy service scenario. At the very least, it can be a potential cartridge sale for the contractor who is willing to stock some of the replacement items and monitor the customer's use.

Of course, any technology has its downside. For highly problematic water, replacement frequencies on disposable cartridge elements may be higher, thus increasing overall operating costs for the user. Sometimes the need for replacement isn't noticed until it plugs up the water flow. Other times, the customers may not notice a change in their water quality or flow. As a result, they may not replace the cartridge element at a prescribed interval even though they should.

However, cartridges offer a diverse arsenal against many water problems-a significant advantage that cannot be ignored. To help you make better decisions, here's an overview of water treatment cartridges.

Basic Types

In a nutshell, cartridges are modules designed to fit in a pressure housing and remedy one or more fluid problems. After a certain limitation is exceeded (time, treatment volume or pressure drop), the cartridge is typically replaced and discarded.

Filtering cartridges come in various forms: pleated, pleated impregnated, string-wound, resin-bonded, melt-blown, granular media, carbon block. Some of these categories have variations on these names.

Pleated filters can be made from various materials. Typically they are made from cellulose (paper) or polypropylene (plastic). In either case, the objective of pleating the barrier material is to pack as much filtering surface area as possible into a compact unit, without sacrificing too much flow. These filters typically have a particle filtering range of 1 to 100 microns, depending on the material, operating conditions and cartridge design. Pleated cartridges are used for sediment removal of varying particle size.

Pleated cartridges can also be impregnated with a media that provides additional function to the cartridge. For example, a common combination would be to combine powdered-activated carbon into a pleated filtering material. This combination can provide particulate matter reduction, as well as taste, odor or organics reduction.

String-wound cartridges are made by winding natural or synthetic fibers tightly around a perforated inner-core tube. The inner string layers experience compression, and thus, have tighter flow spaces, providing a "depth filtering"

Read the Label

One of the most significant discussions surrounding cartridge filters, or any filter for that matter, is the issue of particle removal efficiency. One might assume that a "5-micron filter"


When discussing cartridges, two main standards may be applicable. ANSI/NSF 42 pertains to claims of aesthetic removal, such as taste and odor. It also contains particulate reduction testing, but does not extend into "absolute"