As much as 0.4 inches of rain has fallen so far in parts of Cook County for the storm that began around 12 a.m. this morning. Last night, the Metropolitan Water Reclamation District of Greater Chicago (MWRD) issued an overflow action alert encouraging homeowners and businesses to conserve water, when possible, to provide more capacity in the sewers.  The MWRD is working around the clock to manage this weather event.

The MWRD’s Tunnel and Reservoir Plan (TARP) is protecting the quality of the region’s water resources and mitigating flooding for 3.71 million people served through combined sewer systems. TARP consists of three reservoirs and four tunnel systems. As of 6:45 a.m., the TARP reservoirs are holding nearly 1.4 billion gallons of water. Here is the breakdown:

• McCook Reservoir is approximately 38 percent full, holding 1.3 billion gallons. The McCook Reservoir has 3.5 billion gallons of capacity, serving central Chicago and 36 municipalities covering 252 square miles on the Des Plaines and Mainstream Tunnel Systems. 
• Thornton Composite Reservoir is approximately 1 percent full, holding 0.1 billion gallons. The Thornton Composite Reservoir has 7.9 billion gallons of total capacity, including 4.8 billion gallons of combined sewer capacity, serving 91 square miles on the Calumet Tunnel System, covering the South Side of Chicago and 13 south suburban municipalities.

Before severe storms, the MWRD lowers the levels of the Chicago Area Waterway System at its Lockport Powerhouse to provide added capacity in local waterways. 

“Our staff is managing billions of gallons of water at our seven water reclamation plants and through our Tunnel and Reservoir Plan which is operating to protect our water environment and mitigate flooding,” said MWRD President Kari K. Steele. “As we deal with the fast-changing weather this week, we encourage everyone to conserve water, when possible, to create more capacity in our systems.” 

Learn more about TARP and other MWRD programs 

How you can help prevent flooding

Learn about the types of sewer systems in Cook County

Receive direct Overflow Action alerts via text