Free Guide to choosing an Activated Carbon Water Filter
Activated carbon (AC) has the ability to remove taste odors and a wide range of toxic chemicals in home water treatment systems.
AC effectively removes organic compounds such as volatile organic compounds, pesticides and benzene. It can also remove heavy metals and radon (radioactive gas). As with any single water treatment system, (AC) cannot eliminate all possible drinking water contaminants.
The homeowner must determine which water contaminants are present before purchasing such a system. If you suspect a particular water quality problem have your water analyzed
Whole of house water treatment is now considered essential by most water experts
AC is a black, solid substance resembling granular or powdered charcoal. It is extremely porous with a very large surface area. One ounce of AC has an estimated 20,000 (a football field) square meters of surface area.
Contaminants collect on the surface of the AC in a process called adsorption.
The two main reasons chemicals adsorb onto AC are a ”dislike” of the water, and an attraction to AC. Adsorption of most contaminants results from a combination of these reasons. Many organic compounds, such as chlorinated and non-chlorinated solvents, gasoline, pesticides and trihalomethanes and chlorine can be adsorbed by AC. AC will also remove metals bound to organic molecules.
Fluoride, chloride, nitrate, hardness (calcium and magnesium) and most metal ions are not removed very successfully by AC.
Carbon is not necessarily the same as AC. AC removes far more contaminants from water than does ordinary carbon. Figure 1 shows how contaminants adsorb onto an activated carbon filter.
Figure 1. Diagram of an Activated Carbon Filter.
Home AC treatment systems are quite simple. The AC is normally packaged in filter cartridges or elements and inserted into the treatment device. Water needing treatment passes through the cartridge/element, contacting the AC on its way to the faucet.
AC filters eventually become fouled with contaminants and lose their ability to adsorb pollutants. The filters then need replacement.
Some AC treatment systems are only Point-Of-Use (POU) installed where they treat water used only for drinking and cooking. AC filters can be placed on the end of the faucet, on the countertop or under the sink. Under-the-sink models generally have slightly more carbon and provide better performance than faucet or countertop models however Point Of Entry filter (POE) units have much larger amounts of AC providing greater filtering capacity and much superior economy per liter than faucet, counter top or under sink.
Point of use (POU) systems often have a bypass so water for purposes other than drinking and cooking can be dispensed at the tap without being treated. The bypass increases the life of the AC, however the problems of cross contamination between filtered and unfiltered water is obvious and of concern.
A point-of-entry into the house (POE) system (installed on the incoming water line entering your house) is more appropriate and effective in providing clean and safe water to every tap and shower head in your house.
Consider the volatile organic compounds and radon gas that are examples of contaminants that may get into the indoor air of your house and into your lungs from unfiltered water used for showering and washing. Use of a large (POE) system, which treats water as it enters the home eliminates this potential hazard.
The amount of AC in a filter is one of the most important features. It affects the amount and rate of pollutant removal. More carbon in a cartridge means more capacity for chemical removal, resulting in a longer cartridge/element lifetime. This means fewer cartridge/elements changes and less chance of drinking contaminated water.
Rust, scale, sand or other sediments and organics (protozoa, Giardia, Chrystosporidium)can clog an AC filter. A one micron bag filter placed between the cartridge/element and incoming water solves this problem. When sediment filters become clogged, they need to be replaced or they will cause water pressure to drop.
An AC filter must be deep enough so pollutants will adsorb to the AC in the time it takes the water to move through the filter. The filter depth required depends on the flow rate of water through the filter. The slower the flow rate, the better the removal. The poor performance of small filters such as some end-of-faucet devices is probably due to insufficient filter depth.
Physical and chemical characteristics of the water will also affect performance. Acidity and temperature can be important. Greater acidity and lower water temperatures tend to improve the performance of AC filters.