How does heavy rain impact the availability of drinking water in northeastern Illinois?
In 2019, the Chicago area experienced its wettest May in history, and Lake Michigan was on track to match its record height for June (but missed the record by 1 inch). During this period, a tweet from the National Weather Service elicited some amusing responses, including:
“Too much fresh water. Should be said by no one in history.” @Maltedbarley80
“So, the world’s greatest supply of fresh water has even more fresh [water]. Eat it California!” @EdwardAndersen3
But despite a light-hearted attitude to our seemingly endless freshwater supply, there’s reason for concern—even right here along the Great Lakes. Here’s why.
The Great Lakes: A primer
At the end of the last ice age, our region was left with some of the most fertile farmland anywhere and these huge bodies of fresh water. Combined, the Great Lakes represent about 20% of the world’s surface fresh water; more than half of that is in Lake Superior alone. Most of the water came from melting glaciers when they retreated at the end of the last ice age. According to Peter Annin, “less than 1 percent of that water is considered renewable, that is, recharged by rain, snowfall, and groundwater every year. The other 99 percent was deposited by glaciers during the last ice age”.
The Great Lakes Basin is one ecosystem: Lake Superior flows into Lake Huron at the St. Mary’s River. Lake Huron flows into Lake Erie via the St. Clair River and the Detroit River. (Lake Michigan and Lake Huron are one hydrologic unit, connected at the Straits of Mackinac.) Lake Erie water goes over Niagara Falls into Lake Ontario. And Lake Ontario takes a long trip to the North Atlantic Ocean through the St. Lawrence River. There is a water fountain representing this interconnectedness on display in Chicago. These connecting channels are important to consider because the lakes are always in flux. They are not cisterns designed to store “excess” water. Change is the only constant—the ebb and flow will always continue.
What does this mean for water supply in our region?
Population growth, limits on our diversion, and—counterintuitively—wetter weather will require better stewardship of this precious resource. Lake Michigan is the primary source of drinking water for about 200 communities in northeastern Illinois, serving approximately 80% of the region’s population. With groundwater sources becoming depleted, more communities are exploring using this drinking water source, as well. In fact, a report released by the Chicago Metropolitan Agency for Planning in 2010 projected that demand for Lake Michigan water would grow by 20% by 2050 under a scenario which reflected then-current trends of population growth and development.
Did you know: Rain and snow count against Chicago’s Lake Michigan water allocation?
But we do not operate under a laissez-faire system when it comes to taking water out of the lake. We can’t pump out and use Lake Michigan water at will. Illinois’ diversion of water from the lake is governed by a Supreme Court Decree which limits us to an impossible-to-fathom 3,200 cubic feet per second. (A regulation Olympic-sized swimming pool holds 88,263 cubic feet of water, so approximately 27-and-a-half Olympic swimming pools per second.)
Although it seems like we have the gift of abundance on our hands, it’s not that simple. The Chicago region’s allocation is split into three categories:
1. Domestic water supply which includes public, commercial and industrial water uses;
2. Direct diversion, split between two components,
a. Navigation to ensure navigable depths and lock functions in the Sanitary and Ship Canal system, and
b. Discretionary diversion to improve water quality in the rivers and canals; and
3. Stormwater runoff, which is where it gets tricky….
Due to the reversal of the Chicago River, water which would have flowed into Lake Michigan—after falling from the sky as rain or snow and flowing into local waterways—is now counted against our diversion. That water eventually ends up in the Gulf of Mexico and leads to other issues.
Some rain and snowmelt should flow into Lake Michigan but doesn't because of the reversed flow of the Chicago River. As a result, during wetter months, we use more of our allotted drinking water from Lake Michigan because our stormwater runoff is counted as part of the diversion of use!
Threats to drinking water in northeastern Illinois
Conservation efforts have been effective at limiting our impacts on lake levels, meaning water may be allocated to more communities in the future, especially those which currently rely on groundwater.
During wetter months, we use more of our allotted drinking water from Lake Michigan because our stormwater runoff is counted as part of the diversion of use!
But climate change—especially altered precipitation patterns and higher temperatures—impacts our access to water in multiple ways. However illogical, wetter conditions will spell a greater need for water conservation. Warming temperatures, too, will likely increase water demand. In both scenarios, conservation practices will save more water for domestic uses.
And there is plenty else to be concerned about when it comes to our drinking water, including:
What can we do?
We have a whole lot of water in the lake right now, yes, but that’s no reason for complacency. Now more than ever, our water supply faces urgent threats.
That’s why the Metropolitan Planning Council produced the Drinking Water 1-2-3 guide which details actionable steps that can be taken right now and a host of best practices for elected officials and drinking water operators to ensure communities have safe and reliable drinking water now and into the future.
These threats are not insurmountable, but they will require concerted effort and persistence. While we enjoy an abundance of freshwater in our region, we are not without our challenges and must be vigilant and good stewards of our drinking water sources now and into the future.