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Sediment filters will remove the suspended particles, like dirt, rust, sediments (the stuff you can typically see in the water). They won’t remove anything very impressive like lead, chlorine, microorganisms or harmful chemicals and they generally won’t make the water taste better.

Sediment filters are usually made of a material or fiber wound in a cylinder to block or trap the particles.  Sediment filters are inexpensive, simple and easy to use.  When it turns a funny color or when the water starts tasting like it came from a swamp; it’s time to replace it.

One Micron Filters will remove very tiny particles and some microorganisms like cryptosporidium and giardia.  However, if they are not well designed or maintained, they can’t be trusted to remove those parasites.

They will remove particles 1 micron in size or larger (1 micron = 1/1,000 millimeter).  Our eyes can typically see particles as small as 30 or 40 microns, so a 1 micron filter can remove particles 30 to 40 times smaller than the smallest particle we can see without magnification.

Carbon filters available as granular activated carbon or solid block carbon, will remove or reduce some bad tastes and odors, chlorine, and many organic compounds like pesticides, herbicides and solvents from water.  They can also provide a comfortable environment and breeding ground for bacteria, especially if it is not used regularly. 

Smaller carbon filters might last as little as a few weeks, larger filters can last as long as 1-3 years.  When exhausted (it has removed all of the chemicals it can) it can start sloughing the chemicals back into the water.  It may be difficult for a consumer to judge when the filter is exhausted. 

Bacteriostatic or silver-impregnated carbon filters contains a small amount of silver to keep bacteria growth under control, but they won’t remove or kill bacteria.  The effectiveness of the silver in the carbon filter is questionable, at best.  There is a lack of conclusive evidence that there is enough silver in the filter to really control bacteria, and if you have sufficient silver to control bacteria, the silver might be at an unsafe level for consumption.

Reverse osmosis or R.O. units reduce particles, minerals and metals in water by forcing the water through a semi-permeable membrane. They reduce parasites like cryptosporidium and many bacteria, but won’t remove organic chemicals or chlorine.  They typically have a carbon filter as part of the unit, and some have sediment filters, as well.  They work very slowly - typically making 5 to 7 gallons per day and may waste between 3 and 5 gallons of water for every 1 gallon of drinking water they make.

Pour-through/Carafe style filters use a variety of filters like sediment, carbon, deionization, etc.  They may have a short filter life (typically 35 gallons or less than 1 month per filter) and if the filters are not exchanged, they can re-contaminate the water. 

Counter Top Distillers remove minerals and metals from water by heating the water to a boiling point then capturing steam (water converts to steam but minerals do not and they are left behind).  They remove minerals like sodium and metals like lead and mercury and the high heat can even kill bacteria and parasites. Chlorine, many tastes and odors or organic compounds, like pesticides, herbicides and solvents may not be removed.  The units may be very slow, producing only one gallon in several hours. 

Ultraviolet Light or UVL is not used much in home units.  They can kill microorganisms like bacteria.  The ultraviolet light is dangerous to looked at - can damage eyesight.  Some more complicated home units might use UVL as one of the components.

Water Softeners work by taking out the hardness (calcium and magnesium).  In the process, they raise the sodium content of water (sodium is put in the water in place of calcium and magnesium because sodium doesn’t cause hardness).  They offer no improvement in the quality and taste of the water, but do help detergents work better, and prevent the build-up of hardness scaling.

Other small treatment devices make claims that are too good to be true and almost impossible to substantiate and come with a wide range of costs. Devices are available from magic light bulbs to magnetizers for softening water.

CERTIFICATIONS AND CLAIMS In order to make a claim (such as cyst or cryptosporidium removal, lead removal, chlorine removal, the device should have been certified by some credible agency or organization (i.e.: NSF or Water Quality Association).  Many states, however, have no law or regulation controlling the claims.  The unit may be brand-new during certification testing, although in actual practice, the water quality will decline after installation.  California and Wisconsin have point of use certification programs.

The last word on point of use devices is that some do a pretty good job of improving the taste and quality of the tap water, and some do not.  Do your homework and think sensibly.  Don’t overspend, and if it’s too good to be true, it probably is.