Reply: The health crisis in Milwaukee was caused by an organism called cryptosporidium that was traced to animal waste in agricultural runoff into Lake Michigan. Investigators concluded that a switch in treatment chemicals allowed the bug to survive.

Ironically, the change from alum to polyaluminum chloride was intended as a health preservation measure. The latter is less corrosive than alum, and the Milwaukee Public Works Department switched to it in order to reduce the amount of lead that might leach into the water supply. Unfortunately, they discovered the hard way that the new chemical apparently didn't protect as well against this bug, a relatively rare amoeba-like creature. They have since switched back to alum.

Cryptosporidium is one of a dozen or so organisms commonly found in municipal water supplies. (Warning: Don't read this article during lunch break.) Fecal coliform bacteria are the most prevalent. (I told you!)

Municipal water treatment is a very complicated process involving numerous chemicals and steps. However, even the most sophisticated systems fail to kill all of the bacteria, viruses, protozoa, fungi and other living critters that make their home in the water we drink. Municipal water treatment merely reduces them to levels that most people can tolerate without getting sick.

In general, the public works peoplerks people do a heroic job cleaning up our water. Glitches such as occurred in Milwaukee last April are very rare, which is why it became such a big story. Unfortunately, theirs is an ever-intensifying battle against increased pollution from both organisms and man-made chemicals, sort of like swatting bees around a hive. Also, many contaminants may be introduced into water after it leaves the treatment plant. That's why home treatment systems are some of the hottest selling household products around.

Certain types of in-house filtration systems might have protected against the Milwaukee outbreak and some wouldn't. Safeguarding against all waterborne contaminants, such as cryptosporidium, requires reverse osmosis filtration.

The EPA distinguishes between "treatment" and "purification/filtration." Examples of water purification/filtration are the removal of dirt particles, metals and hazardous chemicals. Examples of treatment include water softening, disinfecting and pH adjustments.

Distillation is the only home-treatment technology that falls under the EPA definition of a bona fide purifier. Distillation in essence boils the water, killing most organisms in the process. However, distillation may not remove all inorganic chemicals, because many chemicals can retain their essential character through liquid and gaseous stages, just like water.

The type(s) of household water treatment or purification/fiation/filtration you may need varies from region to region and maybe even house to house. For instance, well water usually is heavier in minerals than that drawn from lakes, while lakes tend to harbor more organisms. Beware of salespeople who tell you they have a single device that will solve all potential water problems. They are first cousins to the snake oil peddlers of the Wild West whose home remedies supposedly cured everything from cancer to impotence!

In-house treatment or purification/filtration gear can solve just about any water problem. Find someone versed in these basic facts of water treatment and purification/filtration before you rush to buy any equipment for your home.