Sanitary Sewer Downspout Disconnection Program

As of December 6, 2022, the Citywide Multi-Phase Sanitary System Downspout Disconnection Program has been successfully completed by investigating and disconnecting identified downspouts that connected to the sanitary sewer system within the high risk of basement flooding area in Thornhill, Unionville and Markham Village. As part of the City’s ongoing effort to reduce the risk of basement flooding and sewer backup, the City staff will continue to monitor sewer conditions through the annual inspection and monitoring program, review flood reports from large weather event and collect feedback from residents and community to help identify and develop remediate measures for areas with high risk of basement flooding potential.

This multi-phase program was implemented to reduce the risk of basement flooding, and to limit environmental concerns caused by directly connecting downspouts to the sanitary sewer system. These connections increase the flow of rainwater into the sanitary sewer system during heavy or long rain events. This can cause:

The sanitary sewer system to overflow
Sanitary sewer backups
Basement flooding

This program also enforces the existing City of Markham Sewer By-Law # 2014-71 (PDF) [Clauses 3.1D & 19.11]. It also enforces the Region of York’s Sewage and Land Drainage By-Law # S-0064-2005-009, which prohibits the discharge of roof drainage water into the sanitary sewer system.

This program was done in six phases.

Phase 1 Program Area: The first phase of the program began in May, 2013 within the Thornhill area. The investigations and testing work within the Phase 1 Area (PDF) was finished in April 2014. The downspout disconnection work has been finished. Flow monitoring within the area started in Spring/Summer 2016.

Phase 2 Program Area: The second phase of the program began in May, 2014 within the Thornhill Area. The investigation and testing work with Phase 2 Area (PDF) was finished in April 2015. The notice of disconnection was mailed out to affected homeowners in June, 2015. The downspout disconnection work has been finished. Flow monitoring within the area commenced in Spring 2017.

Phase 3 Program Area: The third phase of the program began in May, 2015. It covered areas within Thornhill, Milliken, and Unionville. The investigation and testing work within the Phase 3 Area (PDF) ended in April, 2016. The downspout disconnection work has been finished.

Phase 4 Program Area: The fourth phase of the program began in May, 2016 within the Markham Area. The investigations and testing work within the Phase 4 Area (PDF) ended in February 2017. The notice of disconnection was mailed out to affected homeowners in September 2017.

Phase 5 Program Area: The fifth phase of the program began in May 2017, which covers area within Thornhill and Unionville. The investigation and testing work within the Phase 5 Area (PDF) was completed in November 2017. The notice of disconnection was mailed out to the affected homeowners in Fall 2018 and the disconnection period ended in Fall 2019. Post condition flow monitoring within the area commenced in Spring/Summer 2020.

Phase 5 Expansion Program Area: The fifth phase expansion of the program began in September 2017, which covers area within Thornhill and Markham Village. The investigation and testing work within the Phase 5 Expansion Area (PDF) started in November 2017.

Phase 6 Program Area: The sixth phase of the program began in September 2017, which covers areas within Unionville and Markham Village. The investigation and testing work within the Phase 6 Area (PDF) commenced in June 2018.

Steps taken by City to identify downspout discharge locations

Before any downspouts are disconnected, the City needs to confirm whether the downspouts that go into the ground are actually connected to the municipal sanitary sewer system. To do this, the City takes following steps:

Preliminary property investigation
We do general surveys of residential lots to see whether downspouts are discharging above the ground or into the ground.
Sanitary & storm sewer smoke testing
We do smoke testing within the sanitary and storm sewer systems. This involves blowing a non-toxic, highly visible smoke through the systems and observing the exit points of the smoke. This test finds whether downspouts that go into the ground are connected into the sanitary sewer system or the storm sewer system. The smoke test also identifies other devices/equipment that are connected to the underground sewer system.

Identified downspouts that discharge into the municipal sanitary sewer system

After the investigations and testing were finished, the City sent a Notice of Disconnection to homes with downspouts connected to the sanitary sewer system. The notice showed which downspouts need to be disconnected. More information was provided about how to disconnect a downspout and use rain barrels when the downspout disconnection stage started.

How to disconnect a downspout

Ensure there is a suitable area for the water to discharge from the downspout
Ensure downspouts are disconnected and drained properly away from the foundation walls and directly to a storage device (e.g. a rain barrel), your lawn, or garden.
When disconnecting downspouts, remember not to drain directly onto neighbouring properties, lanes, or sidewalks.
Extend your downspout to discharge water at least 1 metre from any structure's foundation (including your neighbour’s) or public sidewalk, and 2.5 metres from retaining walls.
Ensure the ground slopes away from the house for a minimum of 1 metre.
Use a splash pad to help direct the flow of water and protect against erosion.
Ensure eavestroughs are clean and drain properly.
Obtain professional advice and service from a knowledgeable and licensed roofer, eavestrough contractor, or civil engineer.

Read this Step-by-step procedure to disconnect your downspouts (PDF)

Using Rain Barrels

Rain barrels collect water from downspouts and rooftops and decrease the amount of storm water runoff that leaves your property. Using a rain barrel can help you lower your water bill and improve your lawn and garden.

Learn more about rain barrels.

Contact Us:

Help is only a phone call away! Waterworks staff will be more than happy to help you. Please call us at 905.477.5530.