Page 65 - Spring 2019 Journal

move 90 percent or more of all contaminants in water, including viruses. This viral component is especially important in some situations, such as when traveling abroad or in remote areas where you will make use of water sources of unknown purity. A water purifier is almost al- ways superior to a water filter, but on occasion, a system that is rated to purify water may still leave behind some dangerous contaminants.
In considering the major types of water filtration and purification systems and how they compare, many consumers focus on the exter- nal aspects, such as the location of the water filter—countertop, under the sink, inline or the like—but the location of a filter matters far less than its internal characteristics and its effec- tiveness. Here, I want to focus on the materials and methods of five main types of water filters, rather than on more superficial considerations.
CARBON-BASED FILTERS
This type of system uses a high-carbon
medium to capture contaminants. These filters are primarily or only carbon-based, but other types of filters may also feature a carbon me- dium component. The porous structure of the carbon substrate traps chemicals and other con- taminants. Over time, the carbon medium “fills up” and needs to be replaced. Systems come in both gravity-powered models (such as Brita) or inline (such as Multipure). Some systems have add-ons to deal with fluoride.
Some carbon-based filters use activated car- bon instead of plain carbon mediums. Activated carbon has been treated to increase its porosity. To explain just how porous activated carbon is, note that one gram can have a surface area of over three thousand square meters, or thirty- two thousand square feet!10 So, there are a lot of places for pollutants to get trapped in even a small amount of activated carbon, increasing this type of filter’s effectiveness.
In fact, carbon-based filters vary consider- ably in effectiveness. Some of the most popular water filters on the market (like the Brita or those found on many refrigerators) don’t actu- ally filter much. They are generally just very basic carbon filters, removing some chlorine and chlorine byproducts, and that is about it. The vast majority of low-cost or appliance-
SPRING 2019
based water filtration systems will leave the more problematic water contaminants—lead, industrial chemicals and the like—mostly or even completely untouched. This is changing to some extent because of consumer concerns after incidents like Flint, but older models with older filter technology should not be trusted to deliver truly clean water.
REVERSE OSMOSIS
Reverse osmosis (RO) is one of the most
well-known water filtration options. In a nut- shell, it uses a membrane to capture contami- nants, coupled with pressure to force the water through the membrane. The process suffers from efficiency issues, however, with some of the systems creating about three gallons of waste water for each gallon of filtered water they produce. Some newer RO systems have reduced the ratio to one to one.
CERAMIC FILTERS
Most water contaminants are quite large,
especially compared to water molecules. They are so large that the use of materials with an incredibly small pore size and a large, maze-like structure allows the medium to trap everything from bacteria to lead. This is how ceramic filters work. Many ceramic filters also incorporate silver or a similar bacteriostatic agent to keep pathogens from colonizing the filter medium. The main material used for most ceramic fil- ters appears to be diatomaceous earth, which contains primarily silica.
Ceramic units have one feature that is both a benefit and a drawback—the outer filter sur- face needs regular cleaning to remove built-up surface contaminants. This means the filter often lasts longer than other types, but it also requires that you deal with a surface possibly heavily covered in pathogens (and whatever else the filter collects from your water). So exercise caution when cleaning a ceramic filter!
By itself, a ceramic filter does little to deal with chlorine and some other problematic compounds. As a result, many also contain a carbon core and fall under the next category: multi-medium filters.
Carbon- based filters vary considerably in effectiveness. Some of the most popular water filters on the market don’t actually filter much.
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