Updated studies show that by 2015 some outlying suburbs could face a long-term water shortage according to Crain's. Water supplies are not going to dry up but projections by the University of Illinois Water Survey show that water supplies won't be able to keep up with population growth. As a result, pumping water from them will become cost-inefficient said Josh Ellis, a water policy expert at the Metropolitan Planning Council. He told Crain's:
Communities served by Lake Michigan face the same long-term problem. From drinking water to the reversal of the Chicago River, the Chicago region is now diverting 85% of the lake water that a Supreme Court decision allows; without conservation, that limit could be reached in 15 years.
Recommendations for planning and conservation will be discussed at a forum Tuesday morning hosted by the Metropolitan Planning Council and Openlands, a Northeastern Illinois environmental group.



Your summary is a little confusing, especially with your use of the pronoun "them" in reference to "water supplies," which you follow with a quote about lake water. Pumping will become inefficient in the aquifers outside the lake's basin, while limitations on pulling lake water from inside the basin are legal rather than economic. They're two different issues.
On the upside, it made me actually read the article for clarification.