CBS News Chicago: Even before steady and often heavy rainfall began falling across the Chicago area on Wednesday, the Metropolitan Water Reclamation District was urging people to cut down on their water use, to help limit flooding.

The MWRD handles stormwater management and wastewater treatment in the Chicago area, and issued an overflow action alert on Tuesday in an effort to prevent flooding by limiting how much water goes into the sewer system.

On days like Wednesday, when it's constantly raining, the MWRD water waste control room stays on high alert. Officials said there have been more weather alerts in recent years.

While it might not be the first thing on your mind when you wake up on a rainy day, running your dishwasher and washing clothes are chores the MWRD wants Chicagoans to avoid on Wednesday.

"Also, take shorter showers; anything you can do to make sure we have more space available in those local sewer lines so that water can get to the MWRD," said MWRD president Kari Steele.

The number of overflow action alerts issued by MWRD has been rising.

"It's not that often, but it is picking up more now, because of climate change. We're starting to see more extreme rain events in the Cook County area," Steele said.

The MWRD's Tunnel and Reservoir Plan, also known as TARP or "The Deep Tunnel," is designed to reduce flooding and pollution caused by combined sewer overflows.

The Deep Tunnel system is designed to capture stormwater and sewage that otherwise would flow into local lakes and rivers – or into basements – when heavy rain overwhelms sewers.

TARP has three reservoirs that receive and store the flow from the tunnels during heavy storms.

"Our Thornton Reservoir is just at about 2% capacity full, and the McCook Reservoir is at about 20% capacity," Steele said.

As of Wednesday morning, the Majewsi Reservoir near Elk Grove Village was empty, but with the rain event being unpredictable, that's why the MWRD sends out overflow action day alerts before storms arrive.

"It's very important that we have space available in the local sewer lines so that it can travel to the MWRD and stay out of those unwanted places, like our basements," Steele said.

The overflow action day alert will stay in effect until after the storm ends. Officials typically keep such alerts in place for several hours, or even day or two after a big storm ends since stormwater will continue flowing into sewers long after rainfall is over.

The Tunnel and Reservoir Plan has been around since 1985. It has 109 miles of tunnels, some as large as 33 feet in diameter.

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