Infrastructure that is critical for the everyday operation of condominiums sometimes gets forgotten and overlooked because it’s hiding below the surface. Rainwater, sewage, and groundwater-related infrastructure must be properly managed in a well-functioning condominium. Regular maintenance and check-ups of these systems are required to comply with municipal codes and policies and to ensure the safe operation of a building. 

This article will cover a few key aspects of building sewage and drainage systems and provide condominium managers with a basic understanding of their role in keeping these critical systems functioning.

Decoding What Disappears Down the Drain

When you watch the water drain from your sink or see catch basins collect rainwater after a storm, you probably don’t think twice about it, but not all sewage is the same. Most older buildings have their systems divided into two streams: sanitary and storm. Additionally, some newer buildings have groundwater as a third, separate stream. Each stream is looked at differently by the authorities. 

Sanitary sewage is wastewater collected from various fixtures, including sinks, showers, toilets, and floor drains, which is conveyed via a private, municipal, or provincial sanitary sewer system to wastewater treatment plants/facilities. 

Storm sewage is rainwater and snowmelt collected from roof and site drains and conveyed via a private, municipal, or provincial stormwater sewer system to natural water bodies downstream of a site. Sometimes this stormwater is retained on site for partial re-use or detained on-site to slow the rate of discharge to the municipal sewers. This can be done using a large tank/cistern, or, occasionally, by temporarily storing water on a roof using flow-restricted drains. 

Lastly, groundwater is water that exists underground in the saturated layer of the soil and is generally collected by weeping tiles at the foundation of a structure and directed to either the sanitary or storm sewage systems, depending on the jurisdiction and the quality of the water.

While these three types of sewage are distinct, there are several scenarios where the lines blur, which can confuse managers. Firstly, if an area drain is open to the sky above, on a roof, or at grade, it would be directed to the storm sewer. However, if that same drain were located under a roof structure – such as a covered walkway – it would be directed to the sanitary sewers.

Snow that melts outside drains to the storm drainage system, but snow that is tracked into parking garages on vehicles and melts is collected via sanitary drains. 

To make things more confusing, some localities have combined municipal sewer systems, where both storm and sanitary water are collected in the same sewer within the street. These are no longer permitted to be constructed, but still exist in many older areas. In these cases, the building will have multiple discharge streams, but they may be discharged into the single combined municipal sewer. This sewer, under the street, directs the combined sanitary and storm drainage to wastewater treatment plants, creating a significant challenge for municipalities during large storm events when rainwater can overwhelm the facilities. 

Costs related to sanitary water treatment plants are generally funded via the incoming water bill. That is, the municipality charges you for the fresh water, knowing that most of this water will be discharged back to the sanitary sewers for treatment.

Stormwater and groundwater arrive on the site from nature. For stormwater, there is often no charge to discharge it to the storm sewer system, as it simply flows into the natural water body downstream. Where groundwater is handled separately, it will be metered, and you will be required to log discharge volumes and complete annual chemical testing, all of which will be set out in a discharge agreement. If, due to the chemical properties of the water, you are required to discharge your groundwater to the sanitary sewers, you will pay a significant fee for every cubic meter of water you discharge. In some unlucky buildings, this can result in annual charges in excess of $100,000.

In some cases, there is no excess capacity at the treatment plants or within the local sewer systems, even if the discharging party were to pay a fee. This is one reason that has led to

Toronto’s current Foundation Drainage Policy which does not permit the discharge of groundwater to either the sanitary or storm sewer systems. Instead, these newer buildings must be fully waterproofed below grade so that no groundwater enters the building or they may be required to deal with groundwater on site via a groundwater recharge system. It’s our understanding that the City is undergoing a detailed review of this policy, and revisions may be made in Fall 2026, as it can be quite restrictive to condominium designs.

Understanding the differences between sewage types and where they are permitted to be directed is important for ensuring compliance with municipal codes and bylaws. In summary, there are several key scenarios, and a manager should know which exist in their buildings:

•    An older building with storm and sanitary discharge, where groundwater was likely not distinguished from stormwater at the time of construction. There is generally no discharge agreement. 
•    A building with a separate groundwater stream, where the groundwater quality is acceptable to be discharged to the storm sewer. There is likely a storm discharge agreement, and there may or may not be a charge related to this discharge.
•    A building with a separate groundwater stream, but where the water quality is not acceptable, and the groundwater must be discharged to the sanitary sewer. There is a sanitary discharge agreement, and there is a significant charge related to this discharge.
•    A more modern building where the foundation is waterproofed, and there is no groundwater to discharge.
•    A more modern building where groundwater enters the building but is returned to the ground via a groundwater recharge system
Interestingly, for older buildings, the municipal wastewater treatment regulator typically has the authority to require further streaming of water (such as separating out groundwater) if the building applies for a permit to make significant repairs to their existing system. Although this is currently a rare occurrence, it may happen soon.

Beyond Gravity

Water from the above-grade portions of a building will typically drain to the municipal sewers via gravity. However, below-grade portions of the building are usually unable to drain by gravity, and this water must be discharged using pumps. In this case, the below-grade piping will feed into one or more sump pits located at the lowest level of the site, equipped with one or more pumps, to direct drainage up to the external sewer. 

Stormwater sump pits are usually paired with a settlement pit, where sand and debris can settle out before the water is discharged, whereas sanitary sump pits are usually single pits.

Sanitary sump pits occasionally have macerating pumps to deal with solid waste or a separate grease-separation pit. Additionally, there is sometimes a separate elevator (sanitary) sump pit which may drain directly, or which may flow into the main sanitary sump pit. Lastly, some foundation wall water collection systems incorporate a series of pits around the perimeter of the basement to collect sand and debris that flows in with the groundwater. 

As a result, there can be many different pits in any given basement or garage. Condominium managers need to be aware of the various pits in their basement and know which pit serves which type of water. Settlement pits will require at least annual cleaning to remove debris. All pumps will require routine maintenance, including confirming that alarms are active in the event of pump failure to prevent flooding. Groundwater sumps, particularly those that discharge to the storm system, will need to be kept clean to maximize the likelihood that the water meets the stringent discharge agreements. In addition to sumps, groundwater meters will need periodic recalibration, as required by the municipality or the meter manufacturer.

In addition to the basement sump pits, your building may also have clean-outs and control maintenance holes at ground level. On the surface, these may look like small, plastic covers or larger, cast-iron covers. These features allow for access to observe that sewage is flowing as expected, as well as acting as a starting point for repairs and regular cleaning. They are a vital part of an effective sewage system and should be inspected regularly, as well as after any plumbing work is done, or if any operational concerns are observed. 

In addition to these basic features, more complex systems may incorporate greywater systems and various filtration systems, which are beyond the scope of this article.

Final Flush

While it is tempting to ignore water once it goes down a drain, condominium managers must understand the drainage systems in their buildings to ensure that appropriate maintenance is completed.  

Simon Pignataro is a Professional Engineer with over 8 years of civil engineering experience in condominium and high-rise building projects across the GTA. He is an Associate and Project Manager with R.V. Anderson Associates Limited, who specializes in site servicing, stormwater management, and municipal infrastructure design, and can be reached at spignataro@rvanderson.com

Sally Thompson is a Professional Engineer who has been practicing in the condominium sector since 1990. She is a Managing Director at Synergy Partners Consulting Limited, author of Condo Questions and Answers: Ontario Edition, and can be reached at sthompon@synergypartners.ca
 

View PDF View Flipbook Back to Latest Issue