By T. Jefferson Straub

Summary: With heightened awareness of biological or chemical contamination of our water supplies, ultraviolet (UV) disinfection becomes a stronger consideration for the home. UV shouldn’t be overlooked to provide a safe water supply.

With prices exceeding that of gasoline, why are so many of us reaching for a plastic bottle rather than turning on a faucet for our drinking water? The chic factor explains the trendy labels and why drinking from a plastic bottle gives one the appearance of a person concerned about health. Underlying all this bottled water drinking is a real concern about the quality and purity of our water. Notwithstanding the convenience of having one’s own bottled water, the basic motivation for consumers to buy bottled water remains safety, security and peace of mind.

With the post-9/11 threat of biological terrorism and growing fear of industrial pollution, what can homeowners do to attain peace of mind about the purity of the water flowing from the taps and showerheads in their homes?

Contamination exists in all drinking water. It’s a function of how much, not if it exists. A homeowner should be concerned about three types of water contamination—particulate, chemical and biological. There are basic tests homeowners can perform on their water. Generally, these tests are for dissolved solids and chemicals that can be bothersome and contribute to a bad odor and taste, but which are relatively harmless. Tests for biological contamination are performed by certified labs and can be expensive.

Particulate filters
Almost all but the purest distilled water has particulate matter. Particulates by definition are all undissolved, but can either be macroscopic—visible—or microscopic—not visible. Dissolved solids are often characterized as total dissolved solids (TDS); whereas, TSS describes particulates as total suspended solids. Most homeowners are familiar with the undissolved solids they see in the bottom of a toilet tank or that are caught in the aerators of faucets.

Having grit in water may be unpleasant, but it doesn’t present much of a health hazard. Exceptions are lead and asbestos. Lead can attack the kidneys, the nervous system, and other tissue systems in the body while asbestos has been linked to colorectal cancer. Particulate filtration can eliminate most solids. Types of particulate filters include mesh screens, cellulose cartridges, sand filters and cloth bags, but removal of lead and some soluble particulate often requires microporous filters with adsorbent or ion exchange properties such as carbon block amended with a lead adsorbent. The disadvantage of these filters is they can compromise flow rate and, therefore, water pressure after filtration. It’s important particulate filters be properly designed for each application.

The second type of contamination is chemical. Fertilizers, herbicides, pesticides and industrial chemicals inadvertently (or recklessly) introduced by industry are primary contributors. Removal of chemicals can be simple or difficult. Activated carbon and reverse osmosis (RO) filters can remove many noxious chemicals; however, no purely particulate or biological filter will necessarily eliminate all chemical contamination.

Chlorinated water
Chemical contamination often affects the taste and odor of drinking water, although many chemicals may be passed along without detection by human olfactory senses. Aside from the aesthetic aspects, chemicals can also be hazardous to human health. Ninety percent of U.S. households receive chlorinated drinking water. While most often an effective disinfectant, chlorine also produces a number of by-products such as trihalomethanes that are linked to miscarriages in pregnant women. Chloramines, a chemical mix of chlorine and ammonia, are also a concern, particularly for those on kidney dialysis. Some public health experts are beginning to question chlorination of domestic water supplies and the resulting “soup” of chlorinated chemical by-products.1 Indeed, some health professionals believe chlorine in the water supply may contribute to increased rates of bladder, breast and stomach cancers as well as atherosclerosis.2

Of recent concern is the discovery showering can subject humans to anywhere from six to 100 times the chlorine exposure of drinking chlorinated water. A bathroom shower can atomize water, releasing chlorine in its gaseous form. Unknowingly, we may be exposing ourselves to chlorine gas as we take a shower.

The third type of contamination that homeowners should be concerned about is biological, including bacteria, viruses, yeasts and algae. One of the most common bacteria are coliforms—including Escherichia coli (E. coli)—which are associated with fecal contamination. Although it exists in almost all mammals, E. coli, along with salmonella, shigella, and others not so well known are responsible for many of mankind’s most virulent illnesses including diphtheria, Legionnaire’s disease, typhoid and enteric fevers, dysentery and cholera. Common waterborne viruses also cause polio, hepatitis and influenza.

Another common form of biological contamination are cysts. Cryptosporidium parvum and Giardia lamblia infections cause severe intestinal distress in humans. The notorious travelers’ “Montezuma’s Revenge” dysentery is often caused by Giardia. It’s estimated that as much as 50 percent of the U.S. water supply is infected with Cryptosporidium. Both Cryptosporidium and Giardia are resistant to chlorine. As chlorination can produce potentially toxic by-products and can be ineffective against protozoan and parasitic cysts, additional interest is being shown in ultraviolet (UV) disinfection.

UV disinfection
UV light units have been used for years in recirculating systems for aquariums, aquaculture and in some water treatment facilities to irradiate contaminants, inactivating them by either killing or rendering them unable to replicate. Such devices have been used as sterilizers in hospitals for isolation wards. UV devices are available for home use as well. There are a number of reasons home-owners are turning to UV water treatment devices.

UV disinfection is a natural process. A considerable amount of UV disinfection takes place in waterfalls or rapids of rivers on a sunny day, aided by aeration and its oxidative properties. Water exposed to UV radiation exhibits no change in taste. If you want to enjoy the great taste of water from a spring near your home, don’t chlorinate. Retain great taste and be safe by installing a UV sterilizer.

Homeowners appreciate the low operating cost of UV disinfection—less than that of operating a light bulb. There’s very little maintenance to a UV sterilizer; generally, an annual UV germicidal bulb change will suffice. UV bulbs are available from the manufacturers of UV water disinfection units as well as from specialty light bulb suppliers. UV bulbs may look like ordinary fluorescent light bulbs but are “tuned” for the optimal germicidal segment of the ultraviolet spectrum.

Ratings of UV sterilizers are based on water flow, the intensity of the radiation source, and the length of time water is exposed to the UV radiation. The longer water is exposed to the radiation, the higher the “kill” provided by the UV device. The “kill rate” is described in units of microwatt-seconds (µW-sec)—or milliJoule (mJ)—per square centimeter (cm2). Most bacteria and viruses are destroyed by UV radiation greater than 30 mW-sec/cm². From ongoing research, it appears that dosages in the neighborhood of 100 mW-sec/cm² (or lower) will disable protozoan and parasitic-cyst DNA.

Membrane separation
Another type of filtration device used by homeowners employs reverse osmosis (RO). It uses a semipermeable membrane that can be described as a very fine strainer that removes contaminants down to ionic levels. A water molecule (H2O) is relatively small, and openings in an RO membrane are large enough that H2O are passed through while small enough that complex salt and chemical molecules are not. Cysts are huge compared to water molecules and are generally removed by most RO devices. Some bacterial and viral biological contaminants, likewise, might be removed with RO. Like distillers, RO systems produce “purified” water, but they aren’t averse to biofilm growth. As such, their membranes may be susceptible to microbial grow-through and biological recontamination of product water if not properly maintained. Household RO systems are generally limited to a drinking water spigot and possibly an icemaker. A whole house RO system capable of providing treated water to multiple sinks, showers, etc., is currently beyond the economic reach of the average homeowner.

In the post-9/11 era, many Americans are concerned with chemical and biological terrorism. While hydrochemical terrorism is a possibility, it’s remote. It isn’t practical to introduce enough chemical into a water supply to affect its users. Biological terrorism, on the other hand, is another matter. A small amount of biological material introduced into a water system can multiply and grow to infect the whole system.

What should you, as a homeowner, do? If you’re concerned about your home water, have your water tested. Major water softener companies can test for dissolved solids and chemicals right at your home. Testing for biological contamination will require you to send a sample to a qualified laboratory.

If you notice any visible particulate contamination (sand, gravel or other solid matter), a good, properly sized particulate filter is recommended. If hardness (which generally comes from calcium or magnesium) is a problem, get a water softener. Chemical contamination requires a special filter, but activated carbon filters address many chemical contaminants. Large, national companies specialize in providing soft water. Chemical and particulate filters are generally available at building supply centers and through plumbers.

Finally, perhaps the best defense against common bacterial problems or biological terrorism is for each household to take responsibility for its own drinking water safety and not rely on a central water utility. That means either UV disinfection and/or RO filtration should be in every home. UV disinfection is economically viable to protect a home’s total water supply while RO is practical for a single faucet or water dispenser.


  1. “Is Your Water Safe–The Dangerous State of Your Water,” U.S. News & World Report, July 29, 1991.
  2. Water Filter News:

About the author
Jeff Straub is chairman and chief financial officer of Aquanetic Systems Inc., a UV systems manufacturer based in San Diego. He’s a graduate of Stanford University and earned a master’s degree in business administration from San Diego’s National University. He can be reached at (858) 348-2040, (858) 348-2041 (fax), email: or website:


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