Extraneous Flows (Excess Water)
What is “Extraneous Flow”?
In other places in the Utilities Kingston website, extraneous flow has been referred to more
generally as excess water. The technical and proper term is “extraneous flow” also known commonly
as “inflow and infiltration”. As this is a more technical webpage, it will be referred to herein as
In a nutshell, extraneous flow is otherwise clean storm water or groundwater getting into the
sanitary sewer system. Extraneous flows enter the sanitary sewer by a number of pathways, some
intentional, some not:
- infiltration of groundwater through cracks, unsealed pipe joints and other defects in the
underground pipe network, including the sewer mains, manholes and sewer laterals
- inflow of water from inadvertent cross-connections with the storm sewer system or from
surface drainage in through manhole lids
- inflow and infiltration of water from private-side sources including rooftop drainage
(downspouts) and foundation drainage (connected weeping tile or sump pumps)
Why are extraneous flows a problem?
Extraneous flows are a problem because it takes up valuable space (capacity) in the sewer system.
When it is raining hard, or there is a rapid snowmelt, all of the sources create so much extra water
that the sanitary sewer system can be overwhelmed. When this occurs, bad things start to happen,
such as sewage backups into basements and overflows of sewage into the environment.
What is the City doing about it?
Utilities Kingston has a number of programs working towards reducing extraneous flows. It is
worthwhile noting that unintentional sources are much more challenging to find and fix than doing
the same for intentional sources.
Some of the programs are as follows:
- Combined Sewer elimination (also known as “sewer separation”) This process reduces the
amount of combined sewer, which intentionally collects both sanitary sewage and storm runoff in the
same pipe. Combined sewers are notorious for causing bypasses to the environment and sewer
separation is a key recommendation of the Sewer Master Plan to reduce bypasses. Sewer separation is
scheduled in multi-year road reconstruction plans. The current multi-year plan (2011-2014) includes
elimination of 13% of the remaining combined sewer service area.
- Sewer flow monitoring This process involves measuring and recording the flows in specific
sewers to quantify the severity of extraneous flows coming from the contributing service area. This
helps us to quantify the problem and run programs in those areas to reduce extraneous flows.
- Sewer rehabilitation A considerable portion of the budget available for sewer maintenance
goes towards “trenchless” sewer rehabilitation. This process involves running cameras through the
sewers to identify leaks, and then runs robotic equipment through the sewer that can complete
repairs to fix the leaks. Some of these activities include fixing spot repairs with liners and
sealing leaky joints with grout.
For more detail, visit our What the City is Doing page.
What can a homeowner help reduce extraneous flow?
Homeowners can help a lot! Homeowners can check to see if they have a downspout or sump pump
connected to the sanitary sewer. A leaking sewer lateral can also contribute extraneous flow and
may need repair. These are intentional connections that can be easily identified and fixed. That
is not to say a homeowner necessarily knows they are doing something wrong and that is the purpose
of this educational material.
The primary sources of extraneous flow from private property are the following:
- Downspouts If any of your home’s downspouts go into the ground, they are very likely
directing runoff from your roof into the sanitary sewer system. These should go to the lawn, and in
fact, having them connected to the sewer is illegal as per
These are easy to
find by simply walking around your home and seeing where your downspouts go. They are also
relatively easy to fix.
Visit our Downspouts page for additional information.
- Foundation drainage This is a little bit more complicated and may be harder to
figure out on your own. Foundation drainage is usually either by gravity (a weeping tile system
beneath your foundation) or by sump and pump. These should go to either the lawn or the storm
sewer, but either of these may be connected to the sanitary sewer system which is illegal as per
These may require the help of a plumber to identify. A fix may be relatively
easy, or difficult depending on the situation.
For more detail, visit our Protect Your Home page.
- Leaky sewer lateral The sewage you produce goes to the sewer main in the street by a
pipe called the sewer lateral. The part of this pipe on your property is yours to use and maintain.
It is important to be aware that just like the shingles on your roof, or the flooring in your
kitchen, the sewer lateral is something that will degrade over time. Eventually, it will fail if
you don’t take care of it. A leaky lateral is an indication that your lateral is getting old and
needs to be fixed and is considered good preventative maintenance to avoiding a sewage backup.
Start off by considering having your lateral inspected, and take it from there.
return to top
- Q: If the City allowed downspouts and foundation drains to be connected in the
first place, why should a homeowner have to pay to re-direct them?
- A: Admittedly, this is a reasonable argument to make.
A few points on this:
- The City and/or Utilities Kingston have no authority to undertake work on private
- An analogy: The scientific community now knows a lot more about the impact of automobile
exhaust on the environment, cars in Ontario now require a Drive Clean “E-test” to stay on the road.
Similarly, the utility industry now knows a lot more about basement flooding. With changing
understanding and evolving best-practice, we now know that some things done in the past actually
have negative impacts on a larger scale and need to be rectified.
- Downspouts are usually fairly cheap and easy to disconnect. The City of Toronto formerly
ran a program offering downspout disconnection to its residents. On average, it cost them
approximately $1,300 per home, due to staffing and other costs associated with managing the program.
For the average homeowner, it is likely to cost well under $100 for multiple downspouts. For a
single downspout, assuming basic redirection, the cost is likely under $20 assuming you do it
yourself. Utilities Kingston is choosing to assist financially with the more expensive items (see
- Foundation drain disconnection is more intrusive and more expensive. Utilities Kingston’s
Preventative Plumbing Program is offering to cost-share certain elements of
foundation drainage disconnection in light of the fact it is more expensive to do.
- Q: If homeowners are expected to do more, why shouldn’t the City do more?
- A: Utilities Kingston is doing more.
Over the past few years, Utilities Kingston has been diverting more of available infrastructure
maintenance budget towards extraneous flow reduction. Under these programs, the City is finding and
eliminating the unintentional sources that are usually in the form of small infiltration leaks.
That is not to say they are not important, but one active downspout or sump pump can generate the
flow of many small leaks, and they are easy to find and eliminate.
Downspouts and sump pumps connected into the sanitary sewer are believed to be the biggest
source of wet-weather extraneous flows and it is during wet-weather that sewage backups and
overflows to the environment are most likely to occur.
For more detail, visit our What the City is Doing page.