A complete water purification process can take dirty contaminated lake-water and turn it into something drinkable. In order to explain water purification, you first have to understand that there are many different methods and many steps are needed for completion.
From the wire mesh that removes tree limbs to the point of use filter on the kitchen counter. Each step is important and necessary.
Most of us think of the purification process that is used for drinking safety, but there are methods used for specific industrial, commercial and medical applications. Each has a system that suits it best. To explain water purification methods in great detail is a lengthy process. We can only mention and briefly touch on some of them.
The water purification method that is chosen is largely dependent on what needs to be removed. For de-mineralization and desalination, there is reverse osmosis. For removal of bacteria and other living organisms or "disinfection", there are chemicals, ultraviolet lights and distillation. To remove chemical contaminants, there are activated carbon and multi-media filters.
Ion exchange systems can be used to target any specific contaminant that can hold an ionic charge. Deionization is used to deplete the charge.
The typical process used at a public treatment facility goes something like this. Beginning at a lake or reservoir, the first step is to remove large debris and trash. Wire mesh or other screens can be used to accomplish this goal. That step is pretty easy to understand, but as we continue to explain water purification, the words get longer and a little more complicated.
Pre-conditioning and pre-chlorination is a water purification process that involves the use of chemicals to balance the pH level and prepare the water for disinfection. Flocculation is a term that simply means "to make clear". Chemicals, filters, porous membranes or reverse osmosis may be used in the flocculation process.
Flocculation is usually followed by sedimentation, slow moving storage and final filtration. Chlorine is added near the end of the water purification process to prevent the growth of algae, bacteria, viruses or fungi in the pipes that lead to your home. Finally the water is tested to be sure that it meets with Environmental Protection Agency standards.
To explain water purification from this point on, you must first understand problems that cannot be removed by public treatment or are a result of aging pipes or float into the system on the way "downstream" from the plant. To know exactly what these problems are, a home test can be done. The do it yourself tests are relatively inexpensive, but not as accurate as lab testing.
In our area, one company or another leaves a bottle in the yard every year. I assume they are trying to sell some home water purification, but we have a good one now that blocks anything that could conceivably be a problem, so I never bother with it. That completes my attempt to explain purification from a public treatment standpoint.
For the homeowner, I have this warning. To assume that what comes out of your tap is safe is a dangerous assumption. It is difficult to attribute specific illnesses to low level toxins. The causes of premature births and miscarriages are hard to identify. The cause of a specific type of cancer cannot always be determined. But any of these "may" be caused by exposure to toxic chemicals at low levels over a long period of time.
So, it is reasonable to consider a home water purification process as a relatively inexpensive piece of insurance.