I recently received in the mail the annual water quality report from our local water company, Illinois American Water. I usually only give them a quick glance, but this year I decided to take a closer look.

Even though the Environmental Protection Agency regulates over 100 compounds in drinking water, Illinois American typically only reports on about 20 parameters, some of which are actually not regulated. According to the report, the other regulated contaminants were not detected in the water. One thing to keep in mind is that the concentrations reported are post-treatment, i.e., the water that leaves the plant. Treatment in the Champaign water plant includes iron removal, softening, and chlorination.

The data are reported in separate sections. These include naturally occurring contaminants, such as arsenic and radium, contaminants introduced by treatment, such as trihalomethanes, and contaminants potentially introduced within a home’s plumbing system, i.e., copper and lead. Sodium, which is not regulated, is also reported at the behest of the state of Illinois because it is important information for people on low-sodium diets.

Several values are reported for each contaminant. These include two regulatory values, the MCL (Maximum Contaminant Level), the maximum concentration allowable, and MCLG (Maximum Contaminant Level Goal), which is the level below which there is no known or expected risk to human health. MCLs are typically higher than MCLGs because in some cases the treatment costs to reach the MCLG are deemed too expensive for the expected benefit. The other two values reported are the average concentration (if more than one sample was analyzed) and the range of concentrations detected.

For copper and lead, the report states that 45 samples were collected. It’s not clear to me where these households are or how they were chosen.

Champaign gets its drinking water from groundwater, the Mahomet Aquifer, which is generally well protected from surface contamination. Communities that get their drinking water from shallow groundwater or surface water surfaces often have more contaminants to deal with. For example, East Saint Louis gets its water from the Mississippi River. Their water quality report includes organic carbon, bacteria (measured by total coliform), and turbidity. There are likely many organic contaminants in the Mississippi River that are removed by the treatment processes. Because surface water quality is much more variable than groundwater quality, the plant at East St. Louis analyzes many more samples than in Champaign.

There were no violations of federal or state regulations for Champaign’s (or East St. Louis’s) drinking water in 2010, and I think Illinois American does a pretty good job of explaining the quality of our drinking water. But if you want to know the complete inorganic water quality of the Mahomet Aquifer, you need to contact the Water Survey.