On Tuesday, as heavy rain pelted our windows, some Chicagoans (or at least, Friends of the Chicago River email subscribers) received a direct message: “ACT! It’s an Overflow Action Day.”
But what does that mean?
Heavy Rains = Sewer Overflow
Most sewers in Chicagoland carry a combination of sanitary sewage (read: poop) and rainwater from storm drains. These combined sewers were built before the advent of wastewater treatment technology and once flowed straight into waterways, hence Chicago’s “Stinking River.” The Metropolitan Water Reclamation District — more on that later — added intercepting sewers to carry that water to cleaning plants in the early 1900s. But during heavy rainfall, even in 2025, more water can enter these combined sewers than can be cleaned, causing overflow.
This overflow can pollute waterways and flood banks, streets, and, yes, basements. But there are ways to ease the strain.
Overflow Action Days
When the MWRD declares an Overflow Action Day, Chicagoans should do the following:
- Delay or reduce shower times
- Put off running the dishwasher
- Put off doing laundry
- Replace old or leaky faucets, toilets, and showerheads
In conclusion: You can be a little grody on Overflow Action Days. It's nothing compared to the grodiness of flooding sewage.
Wait, What IS the Metropolitan Water Reclamation District?
You’ve seen the name on your ballot, and maybe you’ve passed right over it. But as former MWRD commissioner Kim Neely du Buclet told City Cast Chicago, “It’s the most important agency that no one knows about.”
MWRD handles water leaving your home — whether through flushing the toilet, cleaning dishes, doing laundry, taking a shower, anything. Meanwhile, water that comes into the home is handled by the Water Department. Think of it as drains versus faucets.
The job of MWRD, essentially, is to make sure wastewater doesn’t go back into the lake, where we get our drinking water. That’s why the agency sets Overflow Action Days. I personally received that update through Friends of the Chicago River, but you can sign up for alerts from the MWRD.
