A recent paper suggests that children exposed to elevated levels of arsenic in their drinking water experienced declines in intelligence [G.A. Wasserman et al., 2014. A cross-sectional study of well water arsenic and child IQ in Maine schoolchildren. Environmental Health 13:23  doi:10.1186/1476-069X-13-23]. Previous studies reported similar results in South Asia and Bangladesh, but this is the first study showing problems in the U.S. Most disturbing to me was that the arsenic concentration threshold above which effects were seen was so low, only 5 µg/L (5 ppb), or half of the drinking water standard in the U.S. and Europe (10 µg/L). The researchers state that the effects on IQ are similar to those found for children with elevated levels of lead in their blood.

There are several areas of Illinois where groundwater concentrations of arsenic exceed the drinking water standard, including parts of the Mahomet and Glasford Aquifers in central Illinois:

While public drinking water systems are required to remove arsenic if it is above the drinking water standard in the raw water, there are no such requirements for private wells. If you have a private well, I strongly encourage you to get your water tested. The Illinois State Water Survey provides an inexpensive service for analyzing water samples that includes an arsenic analysis. If you do have elevated arsenic, the best method for removing it is through a reverse osmosis system.

Here, here, and here are links to reports on arsenic in Illinois’ groundwater.