Historically, ground water supplies were thought to be free of disease-causing organisms because the soil naturally filters them out, But viruses and other microbes from contaminated septic tanks, landfill leaks, or inadequate disposal of animal wastes or wastewater can end up in water beneath the surface, according to Reynolds.
If you draw your water from a private well, you need to study the water cycle diagram, and that will help you decide if you feel safe drinking your water. You should have your well water tested for nitrates and coliform bacteria. But with over 10,000 different possible contaminants, and each contaminant requiring a separate test costing between $20 and $100 each, many people decide it is more cost effective to invest in a high quality drinking water system that is certified to remove a variety of different contaminants.
Some people simply choose to invest in a high quality water treatment system because they want better tasting water, and peace of mind.
That is where your local water treatment dealer enters the picture.