Wet Weather Program



It's all about clean water!


MSD is helping make our local streams and rivers cleaner by reducing sewer overflows.



Would it surprise you to learn that after heavy rainstorms, many of our local rivers and streams contain sewage?


Our public sewer system was originally built in the 1800s and was designed to overflow during heavy rains to relieve pressure on the sytem. It was state-of-the-art technology at the time, but it doesn't meet the needs of today.


Since 2009, MSD has been implementing one of the largest public works programs in the history of our community to improve our collection and treatment of wastewater.


Our Wet Weather Program, which is being implemented under a federal Consent Decree (mandate), is designed to:


  • Reduce combined sewer overflows or CSOs into local rivers and streams.
  • Eliminate sanitary sewer overflows or SSOs into the environment.
  • Assist customers who have experienced sewer backups from the public sewer.



Resolving sewer overflows is not a quick or easy fix.


MSD has embarked on a multi-decade Wet Weather Program that includes hundreds of sewer improvement and stormwater management projects across Hamilton County. MSD is using a phased approach due to the size, complexity, and cost of the 


MSD is using multiple strategies to reduce and/or eliminate overflows, including:


  • Larger Sewers: Allows more wastewater to be conveyed to a treatment plant.
  • CSO Storage Tanks and High-Rate Treatment (HR) Facilities: Allows wastewater to be stored and/or treated at key points within the collection system.
  • Upgraded Treatment Plants Allows more wastewater to be treated through primary and secondary treatment during heavy rains.
  • Smart Sewers Uses sensors and gates/valves within the collection system to store wastewater inside interceptor sewers or direct it to storage tanks and HRTs.
  • Green Solutions Uses dedicated storm sewers and green infrastructure to keep stormater out of the combined sewer system.


Aerial photo looking down at the tops of four large storage tanks
SSO 700 Storage Tanks and High-Rate Treatment (HRT) Facility


MSD has accomplished the following to date:

  • Eliminated 6 billion gallons of sewer overflows, from 14 billion to 8 billion gallons.
  • Completed 150+ wet weather projects, ranging from green infrastructure and dynamic underflow controls to larger sewers and high-rate treatment facilities.
  • Controlled 51 CSOs and reduced/eliminated 44 SSOs.
  • Protected more than 1,000 households from recurring sewer backups.
  • Improved water quality in local streams including the Mill Creek, which is home to nine new fish species.


Photo of a bioswale with a rocky base and pretty pink flowers on both sides
Bioswale at Rapid Run Park


More Info



Follow MSD's progress on reducing CSOs and eliminating SSOs.
Learn more


CSOs, SSOs, and Sewer Backups

What are CSOs, SSOs, and sewer backups and why do they occur?
Learn more


Consent Decree and Wet Weather Improvement Plan (WWIP)

MSD is under a federal mandate to reduce and/or eliminate sewer overflows into local rivers and streams. Learn more