Most of the chemical data that is reported for water is expressed as a concentration. One-Part-Per-Million can be thought of as one inch in 16 miles or one cent in $10,000. One-Part-Per-Billion can be thought of as one second of time in 32 years. It is EXTREMELY MISLEADING to interpret these analogies to minimize the magnitude of the risks. Even minuscule amounts of certain contaminants can poison water!