Abstract: The Environmental Protection Agency says that municipalities must mail out information about drinking water and contaminants (lead, bacteria, etc.).  This document is called the Consumer Confidence Report.  In the report I received, there was no mention of the arsenic level.  Arsenic is a health hazard which can lead to cancers.  In addition, many commercial water filters cannot remove arsenic (cf. lead). In talking to the EPA and also the Chicago Water Reclamation District, I came to the preliminary conclusion that water in Cook County is unlikely to have ``significant'' levels of arsenic.  

The reasons and documentation appear below.

Arsenic not mentioned in Consumer Confidence Report
The Consumer Confidence Report which I received has no information about the arsenic levels even though arsenic is a contaminant which the EPA monitors in the drinking supply.  The reason I initially heard from my own municipality is that arsenic was undetectable in the water supply.

Sources of Arsenic Contamination
This statement was also confirmed by the EPA (1-800-426-4791) and by the Chicago Water Reclamation District.  Both agencies noted that the water which is supplied to the city of Chicago and to a number of suburbs around Chicago comes from Lake Michigan.  Arsenic contamination is primarily a problem with well water which comes into contact with arsenic occurring in the ground.  For this reason, it is much less likely that water from Lake Michigan would have substantial levels of arsenic contamination.  By substantial, I mean exceeding either the old levels of 50 parts per billion or even the newly proposed levels of 10 parts per billion (the new threshold should go into affect about 2006).  

It is also highly unlikely that water once treated in Chicago could pick up arsenic contamination in the process of being transported to the suburbs.  (In comparison, water could pick up lead or copper contamination because of the pipes.  Note again that most water filtration systems are able to remove 90 to 99 percent of lead contamination.)  

According to the Chicago Water Reclamation District, the levels of arsenic which they measured were below detectable levels.  This is less than 3 parts per billion.

For more information.

www.epa.gov/safewater/dwinfo.htm

The site above gives information about municipalities and what violations they may have had in meeting safe water standards.  It also gives information about what these standards are.

Disclaimer
This is my attempt to find out information about arsenic in the water supply for the Chicago area.  I am not assuming any liability for presenting the information I have found.  You should double-check the information I have presented if the subject is important to you.  Furthermore, I also want to point out that some suburbs of Chicago may not get their water from Lake Michigan.  For example, Elgin, I have heard, gets its water from wells.  Thus, the arsenic levels in Elgin may be completely unrelated to arsenic levels in Lake Michigan.