Chemicals found in nature are not necessarily less toxic in drinking water than synthetic chemicals. Many chemicals that occur in nature can be harmful to your health if found in concentrations exceeding the EPA Maximum Contaminant Level (MCL). A few examples are arsenic, radium, radon, and selenium. Nontoxic natural chemicals can combine with other chemicals to produce harmful substances (reaction products). Also, some nontoxic natural chemicals in elevated concentrations, such as salt, can be harmful to your health.
For more information on MCLs see EPA's National Primary Drinking Water Regulations, www.epa.gov/safewater/consumer/pdf/mcl.pdf
