Safe Drinking Water: Filtration
Aisha Ikramuddin
Last Updated: Tuesday, December 16, 2008
How to Choose a Water Filter
After you test your water, if you find that the levels of contaminants are high, you may want to invest in a water filter. Remember, though, that in order for the filter to be effective you’ll have to change filters and maintain the system, otherwise it can actually result in higher levels of contamination.
Types of Water Filters
The simplest, and often least expensive, water purifiers are those that use a carbon-activated filter. These include pitchers with built-in filters as well as those that attach directly to faucets or to plumbing below the sink. Those using granulated charcoal may be slightly less effective than solid block charcoal filters. Carbon filters will generally remove chlorine, coarse sediment, lead and some organic chemicals. The simplest types won’t filter out pathogens, some pesticides and some heavy metals, but those with a combination of filters are more likely to.
The most comprehensive, and most expensive, water purifiers are reverse-osmosis systems. These purifiers push water up against a membrane. The water that does not make it through contains the contaminants and is diverted as wastewater. While reverse-osmosis systems remove a wide-range of contaminants, including all heavy metals, many pesticides and asbestos, they do not remove trihalomethanes (THMs), radon and VOCs, or pesticides such as lindane and atrazine unless they also have carbon filters attached. They also waste a lot of water – a few gallons for each gallon purified is flushed away as wastewater.
Distillers, contrary to popular belief, do not remove all substances from water. Distillers do remove heavy metals, asbestos, nitrates, bacteria, viruses and cysts, but do not eliminate most pesticides, VOCs, chlorine and trihalomethanes (THMs), a group of chemicals which form when chlorine reacts with organic chemicals left in the water by soil and decaying vegetation. THMs may cause miscarriages. In addition, distillation softens water, removing calcium and magnesium, which are beneficial to human health. Softened water is more likely to leach chemicals from storage containers.
Water purifiers that are labeled with "absolute one micron" will filter out cysts that have escaped disinfection by water companies. A word of caution: "Nominal one micron" will not remove pathogens!
The National Sanitation Foundation, a nonprofit organization, certifies water filters by the type of contaminants eliminated. NSF Standard 42 is used on filters that remove contaminants that reduce aesthetic quality (taste, smell, color), such as aluminum, chlorine, iron and sediment. NSF Standard 53 is the most comprehensive, used for filters that remove most pesticides, VOCs, cysts, fluoride, most heavy metals and THMs. NSF has a database of filters certified by them.
Consumer Reports has found that most under sink models are not necessarily any better than countertop units. The magazine regularly publishes ratings of water purifiers.
Regardless of the type of filter you choose, remember to change the filters as often as the manufacturer suggests. Not only will clogged filters be inefficient, but they also may harbor bacteria.
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