In general, our drinking water is pretty good in this country. Whenever people speak about threats to drinking water, usually they are referring to threats from pollution such as solvents, gasoline and agricultural runoff. And, for the most part we can effectively address these risks. But, there are single cell risks out there as well, and they do not get much attention.

For example, have you ever heard of giardiasis? If you are like almost everyone that I know, you haven't. But, you should become acquainted with it because in the last twenty years, this has become recognized as one of the most common causes of water borne illness in humans in the United States.

Giardiasis is a parasite, not bacteria. It is passed from person to person in the waste of infected persons or animals. The symptoms include diarrhea and other intestinal problems. Usually people become sick within two weeks after they are infected and symptoms can last two to six weeks, so it is particularly nasty. Dogs can get this as well as humans.

The parasite possesses an outer shell that protects it and allows it to live outside of the human body for rather lengthy periods of time. So, avoiding infection can be difficult.

It is found everywhere in this country and in the world. For example. if you are a camper who relies on water from a stream, or any water that has not been treated, you are at risk of contracting this disease. Also at risk are childcare workers, because diaper-changing promotes the spread of this disease.

There have also been reports of outbreaks in instances where people have consumed publicly treated drinking water. What this means is that even professional treatment is not a guarantee that your water is giardiasis free.

According to the Center for Disease Control, not every water filter removes these micro pests. Water filtration that uses reverse osmosis or has an absolute spore size of one micron, or that is tested and certified to meet NSF Standard 53 for cyst removal or reduction, appears to be the right kind of filtration system. If you are going to purchase one of these systems, do so from a vendor that understands these issues and can make a trustworthy recommendation.

Apparently, the reason that these parasites are not well suited for conventional water treatment, such as the type of treatment used by public water suppliers including chlorination and ultraviolet light, relates to the fact that they have a cyst stage, which creates a thick cell wall that actually protects them from some water treatment methods.

Some experts recommend that a multiple barrier approach be used. In other words, the concept is to employ more than one protective protocol, used in conjunction with each other, to provide protection. This might include a risk assessment and perhaps land use controls, such as use of appropriate zoning laws. It is interesting just how multi-dimensional parasitic problems can be.

Lab testing can detect these parasites. But, you need to make sure that you ask the lab to check for these bugs -- normal water testing will not include this analysis.

What should you do with this information? Certainly, outdoor-ish readers who regularly drink from streams, etc., should pay immediate attention. It seems to me that you have a real risk here. For the rest of us, we should be aware of the threat and remain vigilant.

The information provided in this column is written by Stuart Lieberman,a practicing environmental attorney, and is for general information purposes only. It is not legal advice and should not be used in place of legal advice.

Stuart Lieberman, Esq., and IRED.Com, Inc., will not accept any responsibilty for any reliance on the information in this column or any damages whatsoever resulting from reading this column.