Well it's true ! Our bodies are 60%-70% water by weight and therefore water purity plays a vital role in our health. Today In the USA, there are about 181,000 industrial waste sites, 16,000 municipal landfills and 100,000 ruptured underground gasoline storage tanks all with the potential to reach the source of your water. This combined with the age and condition of distribution systems, lead based solder used prior to 1987 and older brass faucets, most all water needs some degree of treatment.
Water is the universal solvent and will dissolve and carry with it almost anything with which it comes in contact. Below are listed some of the things water encounters daily, any of which can be present in all water supplies in varying degrees, some being more harmful than others:

Naturally Occurring: dirt, dust, leaves, algae, mold, bacteria, cysts and magnesium and calcium, which cause hardness in water,

Man Made: Fertilizer, herbicide, pesticides, nitrites and fungicide,

Industrial: Detergents, solvents, radio-active waste, acids, hydrocarbon, carbon monoxide, lead based contaminants, and chlorine.

Municipalities are regulated by the EPA, thanks to the Safe Water Drinking Act of 1979, which set maximum contaminant levels for public water suppliers.Water suppliers have done multiple treatments before water even reaches our homes  allowing for far less treatment for the property owner than if we are treating water directly out of the ground, as with home-owners with wells.
Though municipalities are responsible for delivering safe drinking water, private wells in Texas have no state controls on water quality, in both instances it is up to the homeowner to manage the quality of their water.