Metropolitan Water Reclamation District staff work 24 hours a day, seven days a week to protect the water environment, mitigating flooding, managing waterway elevations, and keeping operations moving at its seven water reclamation plants (WRPs). The MWRD treats an average of 1.47 billion gallons of water per day, but that number can soar above 2 billion with intensive rainstorms. On those days, water can surpass local sewer systems for local waterways and never reach the MWRD’s collection systems. After consecutive days of rain, there is increasingly less capacity for the MWRD to hold and treat the additional water.

Fortunately, the MWRD’s 109 miles of tunnels and three large reservoir systems, which comprise the Tunnel and Reservoir Plan (TARP) provide an outlet for billions of gallons of floodwaters. This allows MWRD water reclamation plants more time to treat water before it overflows into local waterways, helping to improve water quality in waterways and protecting Lake Michigan.

One inch of rain across Cook County can yield approximately 16 billion gallons of water, so every drop of water conservation helps during storms.

Prevention Before and During a Rainstorm


You may experience flooding and sewer backups for a variety of reasons, ranging from conveyance of water flow in local pipes, the groundwater table, undersized drainage designs and roof loads, and sump pumps attached to house lines. To help prevent flooding inside or around your home, there are actions you and your family can take before and during rainfall.

  • Pay attention to weather forecasts for your area and make plans to reduce your water use during a rainstorm to help increase the storage capacity in sewer collection systems.
  • Ensure that your gutters and drains are clear to allow water to run freely through them.
  • Consult with a licensed plumber about installing flood prevention tools that can stop backflow water from flooding your basement. These include overhead sewers, check valves, sewer traps and backflow prevention devices. 
  • Consult with a licensed plumber or water proofing company to stop seepage from entering a home by installing drain tiles around the perimeter of the home and connecting to a sump pump to channel water way from the foundation.
  • Inspect your home’s lateral connections for blockages or damage and repair, rehabilitate, or have it replaced to prevent basement backups.
  • Plan your landscaping to avoid root intrusion into sanitary sewer pipes.
  • Ensure your sump pump is turned on and is operating as designed and install a battery back-up pump in case of power outages that come as a result of storms. Avoid discharging sump pumps to the sanitary sewer in separate sewer systems.
  • Eliminate sources of stormwater from entering sanitary sewers in private dwellings by disconnecting downspouts.
  • Consider planting or installing more pervious surfaces to absorb stormwater in place of driveways, lots or other paved areas.
  • Install a rain barrel and connect it to a downspout. You can save and reuse the rainwater. Additionally, consider installing a rain garden.
  • Repair or replace broken or missing cleanout caps.
  • Cover window wells to prevent rain and snow from entering window well drains.
  • Check with your municipality about various cost-sharing programs for flood prevention devices and systems that reduce infiltration and inflow and alleviate the load of water on local sewers.

Whether you live in a combined or separate sewer area, keep stormwater out of sewers to the greatest extent possible by conserving water before and during rain events. To do this, delay showers or reduce their duration, flush less, and wait to run the dishwasher and do your laundry. Every action helps minimize your risk for flooding.

Manage the Flow of Stormwater on Your Property


Earlier this year, MWRD released its first Green Neighbor Guide, which offers private property owners, the general public and landscape professionals proven strategies to reduce flooding, while also improving their landscaping. The guide provides water management tactics to help alleviate flooding in and around homes. Some of the recommended practices include installing rain barrels, bioswales, rain gardens, or dry wells; constructing permeable pavement driveways and paths; and disconnecting downspouts. 

Frequently Asked Questions

What do I do if I flood?

Find the source of your flooding and determine if it is basement back up sewage or seepage. Report your flooding to your local municipality as they manage and operate the sewers that leave your home. Those sewers then feed into the MWRD's large intercepting sewers which then flow to the MWRD’s seven water reclamation plants. Depending on where you live, when the intercepting sewers and plants have reached capacity that water flows into the Deep Tunnel system, also known as TARP or the Tunnel and Reservoir Plan. Please refer to the Illinois Department of Natural Resources Guide to Floodproofing or the Illinois Department of Health for additional assistance.

How can I minimize flooding on my property and in my home?

The MWRD works to manage stormwater, but we can’t do it alone. Residents, homeowners and businesses have opportunities to manage water on their own property as well. One of the easiest ways to capture water is by installing a rain barrel. The MWRD and Openlands partnered to develop a rain barrel installation video. Click here to view. 

The University of Illinois Extension, Illinois-Indiana Sea Grant and Illinois Nutrient Loss Reduction Strategy teamed up to create a video series called Stormwater@Home. This series provides tips to help prevent water from pooling in yards, basement flooding and excess runoff from flowing into local waterways. For more details, click here

Why does my home flood?

Most local sewers are required to carry much more water today than they did when they were first put into service, and as a consequence, they can exceed their flow capacity, causing backups. The May 20, 2020 Chicago Sun-Times editorial makes a good point about how everyone should be thinking about turning their yards into sponges which would allow water to soak into the ground — rather than letting it run off into the nearest sewer line which could then back up into basements during heavy rains. 

How do sewers work and what is a Combined Sewer Overflow (CSO)?

Today, most of the local sewers are required to carry much more water than they did when they were first put into service; consequently, they can exceed their capacity, resulting in backups and overflows due to insufficient flow capacity at some point in the sewer system. A combined sewer system can lead to backups and overflows. This can occur when the intercepting sewers and water reclamation plants reach capacity during heavy rain.

The local sewers in the surrounding communities continue to drain, or overflow, to a waterway. When a lot of rain falls in a concentrated area over a short period of time, stormwater may enter sewers faster than it can flow through them, exceeding their flow capacity. When this happens, some of the combined sewage cannot reach the MWRD’s tunnels and reservoirs or the waterway quickly enough. Thus, it can back up into streets and unprotected basements. The Chicago area sewers are a web of combined sewer systems. Unlike a separate sewer system where the sanitary and stormwater drain to separate pipes, in a combined sewer system, both sanitary sewage and stormwater drain into the same pipes. Please read Understanding Your Sewer for more information. 

What is green infrastructure and how can it help me?

Green infrastructure (GI) is a stormwater management tool that is designed to capture water and allow it to infiltrate into the ground before it enters the traditional conveyance system. In other words, GI is a way to manage stormwater where it falls. These engineered installations store, infiltrate, and/or evaporate stormwater, thereby mimicking the natural water cycle. By using natural or biological modes of controlling stormwater, GI can store water that slowly soaks into the underlying soil. This reduces the amount of water flowing through sewer and collection systems that are often overwhelmed by increasingly intense rain events experienced throughout the region. GI can help to reduce those peak flows and alleviate flooding and basement backups. GI practices can be effective in reducing wet-weather flows to combined sewer systems, reducing combined sewer overflows to local waterways, and reducing runoff volumes and improving water quality. Consider mitigating flooding, protecting local water quality and eliminating run off by investing in green infrastructure at home. Disconnecting a downspout or installing a rain barrel can reduce the load on the local sewer system. Check out the MWRD’s Green Neighbor Guide for additional information.

What is an Overflow Action Alert and how do I sign up?

Launched in 2016 with our partners at Friends of the Chicago River, the Overflow Actional Alert initiative encourages residents to use less water at home when weather forecasts predict significant rain. This allows sewers more capacity to handle increased volumes of water. Overflow Action Days includes a dissemination of alerts that indicate the potential for combined sewer overflows (CSOs) that occur when the MWRD’s intercepting sewers and water reclamation plants (WRPs) reach capacity. The heavy rain overwhelms local sewers, and like a backed-up sink, a CSO will drain and spill out to a waterway. These alerts are used to remind Chicago area residents to conserve water before and during rainstorms. Actions such as delaying showers or reducing their duration, flushing less, and waiting to run the dishwasher or laundry can help reduce the amount of water in the sewer system. For more information about Overflow Action Days, visit here.

What is the MWRD’s role pertaining to flooding and basement backups?

The MWRD serves as the regional authority on stormwater management. In that capacity, our mission is to protect the safety of Cook County’s residents and minimize flooding damage by coordinating, planning, implementing, financing, and operating regional stormwater management projects and to develop and enforce reasonable rules with respect to watershed development. Our goals range from protection for new and existing development from flooding and preventing the loss of water quality and habitat. 

The MWRD also plays a role in managing our waterways to prevent overbank flooding. Our waterway control operators work around the clock to monitor the severity and duration of storms to draw down the elevation of the waterways. We monitor the weather 24/7 using real-time radar and rain gauges. When a storm is predicted, the water level in the Chicago Area Waterway System (CAWS) is lowered by closing the gates at the three lakefront intakes and increasing flow through the hydroelectric generators and sluice gates at the MWRD’s Lockport Powerhouse and Controlling Works. To determine the amount of draw down, the MWRD analyzes forecasts, the geographical area of the approaching storm, soil moisture conditions and availability of storage in the MWRD’s TARP facilities. It can take several hours to lower the CAWS water levels and the process starts well in advance of a storm.

What is the Deep Tunnel and how does it work?

Our Tunnel and Reservoir Plan (TARP) or “Deep tunnel” system is designed to reduce flooding and pollution caused by combined sewer overflows. TARP essentially is a larger intercepting sewer. TARP captures the excess flow from the combined sewers before the water can reach the waterway. This water is stored in the tunnels which is then sent to one of three large storage reservoirs before it is returned to a water reclamation plant for treatment.

What other tips do you have to help conserve water?

Studies have shown that the average household uses about 400 gallons of water per day for drinking, cooking, bathing, washing dishes and clothes, flushing toilets, watering lawns and gardens, and maintaining pools. In the Chicago metropolitan area, we consume nearly 1.4 billion gallons of water a day through residential, commercial and industrial uses—enough to fill the Willis Tower three times over.

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