Clear Waters: Filters to Purify Your Water


According to the U.S. Environmental Protection Agency (EPA), Americans spend billions of dollars every year on home water treatment units. Why? In 2009, The New York Times compiled hundreds of thousands of water pollution records to create a comprehensive national database of water pollution violations; this revealed that laws intended to protect our water supplies were not being enforced, and thus, tap water may contain dangerous chemicals. This database shows that water in Los Angeles contains one contaminant above legal limits and five other contaminants below legal limits, but above health guidelines.

Therefore, water filters are extremely important in water sanitation, which affects overall health quality of the population. There are several types of water filters available with various structures and functions. Read on to learn more about the categories of water filters and how filters purify your water differently.


People use different types of filters depending on the specific composition of contaminants in the local water. Possibilities include harmful environmental runoff composed of pesticides, herbicides, and fertilizers. Fertilizers may contain nitrates, calcium, magnesium, and arsenic. There are also additives in water; chlorine is added to control microbes, and fluoride is added to promote stronger teeth. However, chlorine can react with organic compounds in water to form byproducts that are hazardous to health, and over fluoridation can have long term negative effects on bones and teeth.The pipes that water travels through before reaching your tap may also add dirt, rust, slime, sand, mud, copper, lead, and bacteria. No single type of water filter is able to remove all of the impurities mentioned above, and thus, different types of filters exist.

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Two main categories of water filters are point-of-entry units and point-of-use units.

Point-of-entry units

treat water before it gets distributed throughout the entire house or building. These include water softener tanks for entire houses.

Point-of-use units

treat water right before it is about to be consumed. These include common countertop filters, faucet filters, and under the sink units.

Types of Water Filters

1. Activated Carbon Filter

What is it?: An activated carbon filter has a filter made of granulated carbon or solid carbon filtrate. The carbon particles have a large surface area and have been processed to be very porous. The porous surface attracts and traps dirt and impurities, and the liquid water is repelled and travels through.

Common places of use: Activated carbon filters are used in countertop filters, faucet filters, and under the sink units. They are the most commonly used type of filter.

What it filters: It removes bad tastes and odors, including the smell of chlorine. Some may also reduce the amount of heavy metals, disinfection byproducts, parasites, pesticides, and volatile organic chemicals found in water. According to a 1995 study in Applied and Environmental Microbiology, point of use powdered activated carbon filters significantly reduced bacterial density in rural domestic groundwater supplies after running water through the filter for two minutes.

2. Reverse Osmosis

What is it?: In this filter, water is pushed through a fine semi-permeable membrane, which separates the liquid and the concentrate.

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Common places of use: These are commonly used in under the sink point of use units in combination with activated carbon filters. Water is stored in a pressure tank after reverse osmosis and treated with an additional activated carbon filter to further remove impurities. A 2002 study published in Water, Science, and Technology suggests that there is a higher removal of microbes with the combined system than with reverse osmosis alone. The largest drawback of this filter is that it wastes lots of water; every purified gallon wastes two gallons, so in order to obtain one gallon of purified water, three gallons must be filtered.

What it filters: This type of filter removes most contaminants, including certain parasites, heavy metals, and other environmental pollutants.

3. Ion Exchange

What is it?: Ion exchange filters remove dissolved salts in water by exchanging the mineral ions in water with its own ions.

Common places of use: It is used in house point of entry units and removes calcium, magnesium, and fluorides.

What it filters: This filter “softens” hard water. Hard water contains calcium and magnesium, which may harm pipes and decrease the effectiveness of cleaning agents, such as soap. The ion exchange filter trades these minerals with strong positive charges for those with smaller charges, such as sodium and potassium. According to a 2005 study in Water Environment Research, the ion exchange filtration technique was highly effective in reducing ammonia concentrations and bacterial populations of lake water, resulting in improved health of the overall ecosystem and habitat.

4. Distillation

What is it?: Distillers boil water to create steam, which cools and condenses to form pure, mineral-free water droplets, which are then collected for use.

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Common places of use: This type of filtration is used in countertop or whole house point of entry units and can be combined with an activated carbon filter for further purification.

What it filters: Distillation removes heavy metals, arsenic, fluoride, and other salts.

5. Ultraviolet Disinfection

What is it?: An ultraviolet light may be installed to kill bacteria and other microorganisms.

Common places of use: It is used in under the sink units and is usually combined with an activated carbon filter for further purification.

What it filters: This type of filter removes bacteria and parasites from water. A 2013 study published in Environmental Science and Pollution Research International indicated that point of use ultraviolet disinfection systems used for 20 to 50 minutes were able to inactivate E. coli and eliminate their disease-producing capabilities.

Are They Effective?

  • Look for filters labeled as meeting the NSF (National Sanitation Foundation) standard 53. These filters have been independently tested to prove that they can reduce levels of health-related contaminants. NSF International is a nonprofit organization that tests and certifies certain products to ensure that they meet public health and safety standards.
  • Find out what’s in your water to determine what type of filter to use. Local drinking water information can be found here: If a report cannot be found online, you can contact your water supplier for more information.

Common Mistakes to Avoid

  • Make sure to follow directions in the installation and use of water filters.
  • Follow the timeline for replacement. For example, the smaller activated carbon filters in water bottles should be replaced every two months or 40 gallons. A water filter used for longer than intended may actually start to negatively affect water quality by harboring bacteria.
  • Know what’s in your water so you can purchase the corresponding filter and correct system.

Summer 2013 | Vol. 13 | Issue 5

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