In years gone by, there was a natural water purification process. Rain entered the soil and was cleansed by it. After passing through layers of sand and porous rock the groundwater was clean. Springs and wells once contained water of the utmost in purity. Only open, still supplies had to be considered suspect.

In order to explain water purification, let's look at what needs to be removed, in order to be considered pure. Since the ground has been polluted with chemicals both from heavy industry and agriculture, these chemicals have found their way into the groundwater and so they must be removed.

Bacteria, parasites, protozoa and other microorganisms found in open reservoirs, often cause by farm run-off and biological waste also require treatment. Removing them usually involves a process called disinfection using chlorine. So that is one step in the water purification process.

In order to explain water purification at the public utility level, it is easiest to think of it as a series of steps. Typically, the source is a lake. The water is cloudy, dirty and muddy. There may be leaves, branches, fish, algae and many other substances in it.

First, the lake-water is run through a wire screen that removes all of those large solids. In order to remove the smaller particles in the lake-water, one water purification process that may be used is called flocculation, which literally means, to make clear.

Chemicals are added to accomplish different tasks. Disinfection is one water purification process that can be accomplished through the use of chemicals. Most treatment facilities use this method.

Since ingesting chemicals is unsafe, the water purification process does not truly end until it enters your home and you run it through your own filtration unit. Else, it cannot really be considered pure.

Purity indicates healthy, but chlorine is very bad for your health. Any one of 2100 different cancer causing chemicals may come flowing through your tap. They have been found in the supplies of municipalities around the country.

Federal authorities have said that it does not matter how good the local water purification process is. They cannot guarantee the removal of cryptosporidium, a protozoon that can cause gastrointestinal illness and even death. They also say that testing for it is "unfeasible", so there is no way to tell whether or not it is coming through your tap.

You really have to assume that it is and in order to block it you need a home water purification process that is certified to remove cysts. That is what the critters are called in the early stages of their lives.

That concludes my attempt to explain water purification. As you can see, I believe that the complete water purification process is a joint effort made by local facilities and individual homeowners. Remember, don't throw it on the ground, because it will end up in the groundwater.