What Your Water Filter Really Does

Worried about what's coming out of your tap? Learn how to ensure your water is clean and pure

Water used to be a free and unencumbered resource in our youth, but in recent years it's become public enemy number one. The truth about our taps is probably somewhere in between that glistening image of a pure mountain spring and dark, murky cesspool. Much municipal tap water in the U.S. is fine to drink, but in other communities it bears examination.

Every year your water supplier should send you a report of what’s in your water; keep in mind that these are tests of the municipal water source, and may not reflect contaminants (such as lead) that can enter into your tap after the water hits your house. To learn definitively what’s in your water, the best way is to take a sample to an EPA-certified laboratory and have it tested.

Any number of microscopic impurities can show up in the results, from your garden-variety “solids”—viruses, bacteria and parasites (that cause gastrointestinal ailments such as diarrhea and vomiting);to inorganic chemicals such as arsenic, lead and mercury (that cause, among other conditions, increased blood pressure and kidney problems); organic chemicals such as PCBs (these tend to affect the liver, kidney, nervous and reproductive systems, and increase risk of cancer); and radionuclides (including cancer-causing uranium and radium).

Depending on your local pests, you can simply de-chlorinate, or go for the heavy artillery. The presence of fluoride in water is controversial—some say using toothpaste and getting fluoride treatments is enough and lobby to stop the addition of fluoride in drinking water (a practice instituted in the U.S. in 1940s); others claim it is necessary for dental health. The same debate goes for minerals—while some believe certain filtration technologies that eliminate minerals throw the baby out with the baby water, others maintain there are ample amounts in the average diet.

There are several main types of water filtration, and the best filters use a combination of them. No one filter will get everything. The primary technologies used to clean water are:

Reverse Osmosis
This system, often used by bottled water plants, uses pressure to force water through a fine membrane. Originally developed to produce drinkable water from seawater in submarines, it is recommended primarily for drinking water, as it uses four or more gallons of water per gallon it yields of clear water. Newer “zero-waste” systems return the discarded water back into the home’s plumbing, where it can be used for hand washing, dish washing, showers and other household needs. Reverse osmosis is almost always used in conjunction with carbon filters, which eliminate much of the chlorine that can deteriorate the reverse osmosis membrane. Water is filtered into a storage tank, which replenishes itself as it is used. Although this system yields the best-tasting and best-looking water, it usually requires professional know-how for installation, and can run you anywhere from $500 to $3,000, depending on how extensive your system is.

What it filters out: Reduces most everything, including minerals, fluoride and salts. It produces a result similar to distilled or purified water and is good for homes in areas where sodium, ferrous iron, nitrates, lead, mercury or organic contaminants are present.
What it doesn’t: Does not remove all inorganic and organic contaminants, but because it is usually used with carbon filters, it produces what many feel is the best-tasting (and best-looking) water.

Activated Carbon
Carbon comes either granulated or as a block that filters out most contaminants. Carbon filters vary wildly in their efficacy, depending on their density, or the “micron rating” of its pores—blocks are generally more effective than granules. A carbon filter does not require a storage tank, and even though it will not eliminate some of the total dissolved solids (TDS) that reverse osmosis does, it can be a very effective filter for contaminants and comes in a wide range of forms (pitcher, on-tap, under-the-sink), and therefore is more user-friendly.

What it filters out: Reduces most contaminants, including chlorine, sediment and volatile organic compounds (VOCs) from the water.
What it doesn’t: Any particles smaller than the carbon filter’s micron rating will pass through the filter and into the water, including minerals and salt. It's not effective against some heavy metals, fluoride, chloroform or some microbial contaminants that have dissolved into the water.

This technology, in which fine pores in a tube-like filter catch many organic solids, pre-dates the development of reverse osmosis. This is adequate for water sources that are already of a high quality, is easy to operate and inexpensive to maintain. These units are mostly portable, mostly used for camping or while on the road, but could also be used on a kitchen countertop at home. Water enters the top of the unit and trickles down, much like a coffee maker.

What it filters out: Reduces sediment, bacteria, most viruses and algae (among other substances).
What it doesn’t: Does not remove chemical contaminants or volatile organic chemicals.

Once you've found out what's lurking in your water, you can choose a filter that cleans up the appropriate culprits while providing the best convenience for you and your family. See our guide to water filters to find out which one is best for you.

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