As rain continues to fall throughout Cook County, the Metropolitan Water Reclamation District of Greater Chicago’s (MWRD’s) Tunnel and Reservoir Plan (TARP), which is comprised of three systems, continues to operate as designed.

The three reservoirs are currently holding more than 1.85 billion gallons (BG) of water. Here is the breakdown:

McCook Reservoir is 49% full = 1.76 Billion Gallons
Stage 1 of 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. Stage 2 of the McCook Reservoir will be completed in 2029 and will add 6.5 BG of capacity.

Thornton Composite Reservoir is 1% full = .085 Billion Gallons
The Thornton Composite Reservoir has 7.9 billion gallons of capacity, serving 91 square miles on the Calumet Tunnel System, covering the South Side of Chicago and 13 south suburban municipalities.

Majewski Reservoir is 0% full = 0 Billion Gallons
The Gloria Allitto Majewski Reservoir has 350 million gallons of capacity, serving Arlington Heights, Des Plaines and Mount Prospect across 11 square miles on the Upper Des Plaines Tunnel System.

Before severe storms, the MWRD lowers the levels of the Chicago Area Waterway System at Lockport. We are working around the clock to manage the excess water coming into our seven water reclamation plants throughout Cook County.

As part of the continuing Overflow Action Alert, we encourage the public to conserve water during rain events: wait to run the dishwasher, shower and/or do laundry. Sign up to receive Overflow Action alerts via text. Learn more at our web page.

Learn about the work of the MWRD on our YouTube channel.

Storm Update_081523_2.pdf