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Food Safety News
November 17th, 2009

How to Choose a Filter

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Filtering water at home is cheaper and safer than depending on bottled water. Indeed, as much as 40 percent of bottled water is purified tap water.2 Choosing a water filter can seem like a daunting process, but it does not have to be.

Download or read our Water Filtration Guide online for help in choosing the best filter for your home.

The first step is to find out what is in your water.

For this, contact your local utility and request a copy of the Annual Water Quality Report, also called the Consumer Confidence Report. Every utility is required by law to provide this and usually includes it with a monthly bill. This report will give you information about any contaminant violations in your water system and to help you figure out what type of filtration system is best for your home. EPA posts many of these results on its website.

A quick calculation comparing the average cost of one gallon of tap water, one gallon of tap water filtered with a home filter pitcher, and one gallon of commercial bottled water comes out to:

  • Tap water: $0.002 per gallon 2, 5
  • Average home pitcher filter: $0.10 to $0.20 per gallon 5
  • Bottled water: Ranges from $0.89 to $8.26 per gallon 5, 6

In addition to, or instead of, obtaining the water quality report, you can call your local health department and ask if they can test your water or provide a list of certified laboratories that can.

So once you know whether your water has contaminants, the next step is to find the proper filtration product to remove or reduce them.

Do you want to filter all of the water in the house or just your drinking water? Some people do elect to filter all their water, and so choose a point-of-entry filter, or POE, which typically is installed on your water service pipe just after the meter. However, the majority of consumers select a point-of-use filter, or POU, to treat just their drinking water. Often times these units rest on or under the countertop, and the consumer presses a lever or knob to divert water through the unit for purification. However, many such filtration units come in the form of a pitcher that consumers fill with water and then refrigerate.36, 37

Assuming that you have elected to filter just your drinking water, the next key step is to decide what kind of filtration technology you need in that counter top unit or pitcher. Before buying, though, make sure your product choice is independently certified for design, material safety, and effectiveness for the contaminants you want removed. The most notable and well-regarded organizations (all non-profit) that test and verify water treatment and filtration products are:

Adsorption filters are the most common. They usually employ activated carbon or granular activated charcoal to remove or reduce chlorine, particulate matter, and organic contaminants such as pesticides. The technology works by attracting and holding certain chemicals as they pass through the carbon block. Prolonged use clogs the filter and renders it less effective, so it must be changed according to the manufacturer‚ instructions for best results; failing to change a filter can even reduce the water quality because of microbial growth and/or breaks in the filter. Some also remove disinfection byproducts.36, 37

Many common adsorptive carbon filters include an ion exchange resin to reduce or remove lead and other heavy metals. Overall, these filters tend to be economical and effective for most people‚ needs. When purchasing such a filter, read the package to make sure the product meets the National Sanitation Foundation/ American National Standards Institute standards. The NSF/ANSI standard #42 applies to filters that deal with taste and odor, while standard #53 applies to chemical contaminants.36, 37

A particulate filter, also called a mechanical filter or micro filtration unit, screens out physical particles from water, such as small amounts of sand or even some bacteria, and pathogens, including Giardia and Cryptosporidium. Particulate filters should not be relied on to disinfect water with high concentrations of bacteria or viruses. These tend to work best in combination with adsorptive carbon filters.36, 37

glass of waterIn contrast to adsorption filters, reverse osmosis, often called RO, pushes water through a membrane with microscopic holes that allow only water molecules to pass through, while trapping certain chemicals and minerals. These units remove hardness, nitrates, sodium, dissolved metals, like lead and copper, some organic chemicals, arsenic, and fluoride. Because the membrane is delicate, some units are sensitive to chlorine and have a chlorine removal step before filtration. Not all organic chemicals are removed so often there is a secondary adsorption filter after the membrane. Examples of organic (carbon-based) chemicals include benzene and the insecticide atrazine.36, 37

Reverse osmosis is not very water efficient, meaning it can take more than one gallon of water to produce one gallon of purified water; the “lost” water is sent to the sewer system. Due to the inefficiency of the unit, RO is usually just used for drinking water and is installed below the kitchen sink. The unit is usually large, so consideration should be given to space. The startup cost of an RO unit can range from $300 – $3,000 or more. After purchasing installation and maintenance costs are required. It is important to maintain the membranes as poorly maintained filters can reduce the quality of your water. Look on the package to see that it meets the NSF/ANSI #58 standard.36, 37

Distillation units boil water and collect the steam in a separate chamber. Distillation removes some organic and inorganic chemicals like hardness, nitrates, chlorine, sodium, dissolved metals, fluoride, and more. You must make sure the unit is specifically designed to remove organic chemicals, including various pesticides, because they can pass through the unit with the steam and contaminate the remaining water. Distillation units are usually placed near the kitchen sink and have separate faucets. Distilled water is highly effective, but also energy intensive and expensive. It can take up to four hours to produce one gallon of water. Many people also say the water tastes flat since it lacks the minerals that give water taste. The NSF/ANSI standard for distillation units is #62.36, 37

Some important precautions that must be considered with filtered water:

  • When you filter your tap water you are taking out the disinfectants that prevent microbes and bacteria from growing. It is best to keep your filtered water in the refrigerator and treat it like stored food. Dont wait too long to drink it!
  • Remember to change filters as the manufacturer recommends. A water filter left in too long reduces the efficiency and can even harm water quality. You may even notice a chlorine taste in the water.
  • If you are on kidney dialysis, pregnant, or have a compromised immune system talk to your doctor about the type of water filtration system to use. Bottled water is not necessarily the best choice. Make sure the filter is rated with an absolute one-micron filter.

For footnotes, see Take Back the Tap.