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What You Need To Know About Septic Systems Before Purchasing A Building Lot in Ontario


Planning to purchase a lot to build a home in Ontario?

Before you do anything else, check if a public sewer system is available? If not, you will need a septic system to treat and dispose of sewage from the home you plan to build.

What type of septic system you will need, how it will be designed and constructed depends on the particular lot, how much space you have, the characteristics of the surrounding land and the make-up of the soil.

Whatever type, all septic systems require careful attention to design, construction, operation, and maintenance.

The septic system typically consists of a septic tank buried in the ground and a drain-field that can fit within the front or back yard of the home-site.

Septic Systems in Ontario

Septic System

Household discharge from the kitchen, bathrooms, and laundry room flow directly into the septic tank where the solids are retained and separated from the liquid. The liquid waste flows out of the tank through a series of pipes to where it is slowly released into the leaching field where it leaches through the soil and is purified before reaching the groundwater.

The leaching bed is made up of porous materials, such as sand and gravel, and acts as a filter to clean the water before it seeps back into the ground.



Light solids, such as soap suds and fat, float to the top and form a scum layer. This layer remains on top and gradually thickens until you have the tank cleaned.

Unfortunately, not all soils can absorb wastewater or purify it.

Septic systems that are installed in unsuitable soils usually malfunction by leaking raw, untreated sewage to the surface of the ground or a roadside ditch, or by contaminating the groundwater. The sewage may contain deadly bacteria and viruses.

It can be expensive to remedy the odor problems and potential health hazards that result from the use of septic systems in unsuitable soil.

Because of that, the Ontario Building Code requires an expansive soil and site assessment by the local health department to determine the suitability of the soils and topography of the lot.

Setbacks For Septic in Ontario

Setbacks For Septic in Ontario

Reviewing the Lot

If a septic system is needed, walk over the lot and look for indications of soil problems or site limitations that could affect the performance of a septic system.

Consider the following before you purchase a lot:

  • Is there enough space on the lot for the home, the septic system, and water well (if needed)?
  • Is the land next to a stream or river that could flood it?
  • Does the area seem wet and swampy?
  • Is there a bedrock that can interfere with the septic system?
  • Determine the type of soil on the lot by digging a two 5 foot holes where your field is to be situated
  • Find out what type of septic system, if any, will work on those soils.
  • Obtain a cost estimate for installing the kind of septic system you need.
  • Ask about the operating requirements and maintenance costs for the system.
  • Your well and all neighbors’ wells should be 100 feet or further from the septic system.
  • There must also be enough land for a “repair area” that can be used if the system needs expansion or replacement in the future.

Septic Systems in Ontario

Part 8: “Sewage Systems” of the Ontario Building Code (OBC) regulates the design, construction, operation and maintenance of on-site septic systems for most single-family homes. In most areas, the local municipality’s Building Department examines plans, issues permits, and does inspections for systems regulated under the OBC. In some regions, this approval responsibility has been delegated to local Conservation Authorities or Health Units. The Municipal Building Department will be able to redirect inquiries.

Proper approvals under the OBC must be obtained by the homeowner before installing any of the suggestions for improving system performance.

The capacity of the Septic System

The two primary elements that command the size and complexity of a system in Ontario are the maximum amount of wastewater that the building could produce on a daily basis, and soil/site conditions.

Case in point; a small one-bedroom /one-bathroom house would have a maximum daily flow rate of about 750 liters.  If that system were being located in soils with a high absorption rate, then the system could be quite small and be installed at a reasonable cost.

On the other hand, if it is a huge five bedrooms home with a maximum daily flow rate of 2500 Liters and clay soil (which can only absorb 4 liters, per square meter, per day) then the cost could be enormous because a lot of sand would need to be trucked in.

It is almost impossible to determine how much a septic system is going to cost without visiting the property to assess the available space, access for large equipment, cleanup needs, etc.

The capacity of Septic System in Ontario Explained

Types of Septic Systems

The kinds of soil and site conditions on the land determine whether the local health department can issue a septic permit, as well as the type of septic system needed there.

The conventional septic system, with a septic tank and a number of trenches buried 2 to 3 feet deep, is used at almost one-half of the homesites with septic systems in Ontario.

It works well in brightly colored (red or brown), thick, loamy-textured soils with deep water tables. This type of system is relatively inexpensive; the average installation cost ranges from $7,500 to $10,000.

On some soils that are too wet or too shallow for a conventional septic system, a modified standard system or an alternative septic system may be used.

Clip Art Graphic of a Yellow Residential House Cartoon Character

Advanced Treatment Systems – Alternative Septic System

If a conventional system cannot be used, you may wish to determine the installation cost and maintenance costs of the alternative septic system that can be used.

Advantages of alternative systems:

  • used on sites not suited for conventional septic systems
  • need much smaller septic fields
  • have the potential to remove significantly more bacteria and organic material than a conventional septic system
  • may extend the life of an existing leaching bed
  • take up less room in the yard
  • may reduce nutrient output (depending on the type)


  • more expensive to purchase and install
  • are more costly to operate than a conventional septic system (electrical costs, media replacement)
  • includes more mechanical parts that can break down or need replacement
  • requires mandatory maintenance (increases costs)

You may want to consider alternative septic systems when:

  • coping with lots with inadequate conditions for conventional systems
  • dealing with lots that can’t accommodate the size of a regular bed
  • replacing an old failed septic system
  • building on hard-to-access lots where transporting materials for conventional systems is costly and difficult
  • if you want to provide additional nitrate reduction that some of the advanced treatment systems provide

There are many soils that are not suitable for an alternative septic system either.

For these reasons, it is in your best interest to determine the suitability of a lot for a particular kind of septic system before purchasing the lot. If you can use a conventional system, ask about any modifications to the system or to the site that may increase the installation cost.

Also, ask whether the approval affects the number of bedrooms that can be built in the home, or the location of the house, driveway, or a swimming pool.

In any case, it is a good idea to make the purchase of a building lot conditional upon the issuance of a permit for a particular type of septic system.

  1. In your article, you stated that household discharge from the kitchen, bathrooms, and laundry room flow directly into the septic tank where the solids are retained and separated from the liquid. My wife called me this morning because she noticed a really bad smell coming from the drain in our sink. Are there certain kinds of septic tanks that need maintenance or pumping more often?

  2. I want to make sure that I get the right kind of septic system. It makes sense that I would want to ensure that I get the right kind of system in the first place! It seems like I would benefit most from an ordinary system.

  3. Derek, what kind of system do you currently have and when was the last time you pumped? It’s tough to say which systems will require less pumps than others since it depends on what is thrown down the drain. No matter which system you have, habitual monitoring and maintenance will always be the most cost efficient and the best route in terms of longevity of the system.

  4. Gentlemen:

    Is it possible to convert from a holding tank to a septic system? I believe the tank is a concrete 2500gal capacity.

    The tank is in the front yard – there is virtually no backyard.

    The property is in Whitchurch-Stouffville area.


  5. We are looking to relocate our tile bed to another area on the property. What can we do on top of the old tile bed? Would like to put a garden in but not sure that will be ok on top of an old septic field. All our annual tests have come back showing potable water flowing into the septic field.

  6. I had a septic inspection done on a home I was buying from a Septic Inspection Company.
    They could not locate the septic field…it is under my garage. The tank is under my dining room, a flow test was done for 50 minutes, based on no issue with a flow test, they suggested installing risers for easier access in case a winter pumping was required.
    I have since found out…as my entire home smells of septic fumes, and the earth under my dining room and addition smells of septic (breath taking).
    that the tank is also too small for the size of the house and there are other non code issues with the tank. Trying to find a company to come and pump it is challenging, found a company but it took 2 guys, there are 2 cement lids weighing about 300 lbs each. The septic company and their insurance company refuse to come good for this poor inspection to say the least…my entire home for 2 years has smelt, it goes from unbearable to moderate. Is the inspection company liable? not sure if I can ask this but it’s been a long go no where road with this company denying responsibility. Thanks for anything you can offer as advise. Yes I have contacted my Municipality and South Nation Conservation(who are more than aware of my situation, as they have been to my home, but refuse to issue work orders. Thanks again

    • This is like a scene from the horror movie. Are you kidding me? You bought a house built over the septic system??? Call a lawyer. There are too many questions unanswered. Who knew? Did the previous owner sell it knowingly? Did the real estate agent know the situation? Was the inspection company aware and sold you the house anyway?
      You need to decommission the old septic and build a new one.
      Also, it is unhealthy and forbidden by the health department to live on the top of the tank or the system. Once more, seek legal help. In the meantime, I would stay out of the house.

      • I’ve contacted local health unit and informed them of illegal waste pumping into ditch. Also told them about the house being built on top of the septic tank. They have had some serious health issues that could be the cause of the gasses you can smell in the house. Local health unit person said he didn’t think that it is illegal to have septic tank under the house. It has been over 3 months and nothing has been done. Is there someone i can contact regarding this issue because we both have a well and I really don’t want this happening this close to my house. Thank you.

        • Your questions are not very clear;
          1. I’ve contacted local health unit and informed them of illegal waste pumping into ditch. Where is this? Who is pumping? Is it your ditch? What kind of waste are they pumping?

          2. Also told them about the house being built on top of the septic tank. Are those two different problems? Is it your tank?

          3. They have had some serious health issues that could be the cause of the gasses you can smell in the house. Who are they? Are “they” the members of your family? Which house, yours or theirs?

          4. Local health unit person said he didn’t think that it is illegal to have septic tank under the house. Answer: That can not be true. No competent septic inspector will tell you that.

          5. It has been over 3 months, and nothing has been done. Answer: I do not know what exactly do you want to be done. If someone is building a house next door to you, the house and septic have to go through inspections. If all the inspections pass, it is not your business to stick your nose into their building, unless they somehow influence your property.

          6. Is there someone i can contact regarding this issue because we both have a well and I really don’t want this happening this close to my house. Answer: I do not know how far is “this close to my house”? Drilled well in Ontario has to be at least 50 feet away from the septic system, and dug well has to be 100 feet away. If those criteria are met all is good and legal.

  7. Sorry, 1. Neighbors are pumping raw sewage with a grinder pump directly from septic tank their tank which is located under the house, this is un organized township in Ontario. 2. Actually built an addition over septic tank. 3. They have. 4. Very true,I spoke to him in person. 5. Existing tank and field. 6. Theirs is a dug well from many years ago and is nowhere near 100′. In closing, because of what the guy from the health unit told me, that’s why I was asking who else i could contact. They the neighbors seem to pump out the tank during a rain. Thank you.

  8. I am in rural Ontario and have aseptic system, 10 year old house. We see the septic field, a little elevates. And where the septic tank is, there is a post, with an electrical outlet, a plug in attached, and we hear a motor running just a foot past the septic tank, between it and the field. What is that motor? Does it pump the sewage to the field? Is it automatic or run continuous?

  9. Hello, we just built a new cottage with new septic tank provided by the builder. A friend of mine mentioned that there should be an overflow alarm built into the cottage or somewhere to notify us. I have looked everywhere to find out the answer to no avail. Is this an after market option or is this suppose to be supplied when the septic tank was built.

  10. I have a bed that needs to be replaced. It’s been in the same location since 1958. I am told now I have to install a holding tank,because the bed is to close to my dug well witch has also been there since 1958. Is is also about 50′ away. Do I have any legal rights?

  11. I have a 90′ run of pipe from my septic tank to the leaching bed/field. Can I put an above ground pool over part of the pipe? It runs diagonally across my back yard, under a seldom used driveway and into the front yard. We have a sketch from the contractor who installed it but there are no measurements or landmarks indicated so we don’t know precisely where the pipe lies or how deeply it is buried.
    Thanks for your help!

    • Can I put an above ground pool over part of the pipe? The short answer is no. Placing a pool on top of a leach field can crack or crush the pipes or compact the soil enough to prevent proper drainage.

  12. I have a shore well . How far foes a septic mound have to be from it?

  13. Hello,

    The septic pump at our cottage home seized sometime in February and the tank froze (not sure which happened first). It has just thawed and I am wondering if the tank could be better insulated. Is it possible to do this? I also noticed the pvc pipes running to the septic bed are 1.5 inch – is that an adequate size?
    Thanks for your time,


    • I do not quite understand which tank froze? Pump tank or sewage tank. The septic system records should be available in your township or your health dept.

  14. I would like to create a covered concrete patio off the back of my home to replace the existing 15 year old deck built when the house was new. My effluent tanks are very close to the side of the deck now and a new poured pad would also be very close. My question is how close to the tanks am I permitted to build/pour a pad? (I have a 3 tank system with a raised bed)

  15. Was wondering if you need a working Septic to sell a lake front cottage, so long as you disclose and discount price for the repairs needed, can you sell the cottage “ As is”?


  16. Our tank has a crack in it. Can we simply replace the tank? The field was inspected and it is fine.

    • Probably. Talk to your township’s septic system inspector. You will need a permit.

  17. Question… I have a fence with post (3ft deep) between the runs (5ft spaces) is that allowed?

  18. Can a new weeping bed be put in the same place as the old one.?
    Thank you

  19. can’t find this info anywhere.
    How far does my contained holding tank have to be located from a creek?

  20. I have a questions about a flow test for the septic field. We had our tank pumped out in the Fall in prep to sell home and to determine if we might need to deal with any issues prior to sale. Everything looked fine at that time and we`ve been experiencing no problems.
    In May we had a flow test done for an interested buyer and it failed. When we opened the lid the tank was full of water.
    My question is this: This Spring was accompanied by record rainfall, and at the time our ground had been particularly saturated for about 2 months. If the ground conditions are that saturated, can they impair the flow test?
    Conditions are much drier now, so we’re debating if we should do another one.
    Thank you kindly

    • You probably have the right reason for the failed flow test. Done at this time, it would probably pass. However, what happens if we have a record rainfall next year and the year after? Do you really want to sell the house with a septic system that can fail at any moment? Try contacting a qualified septic installer in your area.

  21. Is a valid septic inspection required to complete a land transfer of property in Ontario?

  22. Bought a 3 acre property in Norther Ontario on the lake. It’s undeveloped land that I hope to put Tiny Homes and Glamping sites with plumbing. I will start with 5 and add more until I hit 30 sites. Most of the property is on bedrock and almost impossible for a septic bed or buried tank. Am I able to have an above ground storage tank that gets pumped out regularly? I assume that I can pump multiple sites to one tank?

  23. I am curious to the answer for Jeff. Wonder what his options are? Would he use a surface discharge system? If so, how can we get them to agree to one of these over a conventional system?

  24. Good evening.
    Will a open bottom ecoflo peat moss system work in soil that is T50?

  25. Thanks for explaining that if you put a septic tank in unsuitable soil it can be expensive to remedy the odor. I have a spot on my property where I have wanted to put a septic tank for years now. I have no idea if the soil there is suitable to not so I’ll have a septic service come out and test it for me.

  26. I bought a two bedroom farmhouse that requires a new septic system (holding tank and field). I’d also like to convert the small insulated barn into guest quarters. Can two buildings share the same septic system in the St Catharines area?

  27. Hi
    We currently have a small older cottage that has a holding unit. We would like to upgrade to a septic bed. How far does the bed have to be from the lakefront? We are in the Porcupine and District area in an organized township.

  28. Do I need to do anything to continue to use a previously installed (20 years) high quality 2250 litre holding tank (designed for pump out, no septic characteristics, very high industrial-quality pvc) for a small seasonal cottage using an RV style toilet, no dish water or shower, just a hand sink? Would this be a grandfathered installation? The area was an unorganized township absorbed into a town after the tank was installed.

  29. I would like to put an inground pool in my yard. Is the 5m measured from the septic bed to the wall of the pool or to the edge of the concrete around the pool?

  30. hi everyone… so i need replace my leach field.right know he is on hill and every time i used a washer machine or dishwasher when im outside i can feel that bed smell a.but i only have space near of my house .i want know if ido there i will feel that smell or when my kids are playng they will smell

  31. Can a fence be built between the septic tank and the field? We had an old fence that was blown down from a storm. Wondering if it’s safe to do that or if I need to go around the entire field

  32. need a septic tank for my new house
    It will located in Lancaster ON
    my phone:514-9278768
    Thabk you

  33. I have a question for you;
    We just purchased a home on septic, the septic drawing outlines the 4 tanks and the leaching bed but it also has a larger area as a reserve tile bed.
    I can not find any information on the reserve portion, is this a required part of the septic system?
    Thank you

    • No.

      • Thank you for your quick response!
        Just to clarify; since it is not a required part of my septic system, am I able to use this area for a patio/ in ground pool? Do I need to keep a designated area as a “reserve bed” for the just in case scenario?
        Thank you again!

  34. 1. Retaining Wall & Septic Mound
    We have a raised septic mound in the backyard. Near the bottom portion of the slope, we are hoping to put an armour stone retaining wall (about 22″ high). How close can this wall be to the closest pipe in the septic field? The mantle is on the other side of the septic system and would not change at all.

    2. Deck & Septic Tanks/Piping
    We are hoping to put a covered porch on the back of our house and also have a raised septic system in the backyard. The effluent pipe for the septic system runs from the back of the house to the tank. Are we able to straddle the effluent pipe with deck footings?

  35. Are you allowed to hook up your rainwater sump pumps to go through the septic system or should that be pumped out to the front ditch ?

    Can your septic pipe be drained into the neighbours back yard thus causing it to be so saturated that it is impossible for them to cut their grass ?

  36. Hello, my wife and I are planning to build a secondary dwelling (in-law suite) which will be connected to our existing septic system. This will increase the amount of daily flow which will potentially require us to upgrade the capacity of our existing septic system.

    Question : Will a brand new system be required by default, or can we evaluate with Engineering firms to option to add runs to our existing system to save on cost?



  37. I appreciated it when you shared that it is great to find out about the right type of septic tank that is suitable for the type of soil at your home. My uncle just mentioned the other day that he is planning to build a house on a plot of land that he recently bought last year. I will suggest to him looking for a reliable service that can help install a septic tank for his new home.

  38. It’s great that you talked about septic systems and their features. Recently, my wife and I decided we want to build our dream house from the ground up. We’ve heard a little about septic systems and how they’re a cost-effective option in the long haul, so we’ll be sure to look into them. Thanks for the information on septic systems and their costs.

  39. It’s good to know that you need to have enough space. My husband and I want to look into getting a septic tank for our home. We’ll make sure to keep these tips in mind once we find a professional that can install a septic tank for our home.

  40. Hello, A residence on the road next to us is cutting away one side of his raised septic bed. It looks like he did it to make a road or pathway to his house. Is it legal to take away a portion of the side of the raised mound?

  41. What are the the fixes if a septic was placed to closed to a drilled well
    It was installed with a permit

    It’s on of the newer small ones with the filter of bark ontop

  42. Wondering what the minimum lot size is for a septic system? We have had septic with our past two homes but both had acreage. We are currently looking at a 1/2 acre lot and there is no sewer or city water so we would have to install septic and cistern. We’ve always been under the understand you need 1 acre for a septic system. Please advise! 🙂

    • Check with your neighbours. They must have some kind of septic system. There is no minimum size of the lot. The smallest filter bed can be 5M x 5M. Depending on the size of your house, you can put it on a small lot. You have to have 5M setback from the house, 1.5M for the tank, but it is possible on 1/2 acre.

  43. We are looking to purchase a vacant lot that previously had a community centre on it. There is a current septic and drilled well on the lot (septic installed in 1997, pumped in 2021 and visually inspected) Do you happen to know if its possible to use an older septic with a new residential building? Township will not return our calls.

  44. Was wondering if a permit is required to repair my weeping bed someone drove over and pretty sure pipes are broken

  45. Without septic pumping, the sludge will eventually build up and cause two serious issues. First, the sludge can start to block the drainage from the home and begin to back-up the sewer lines. This will clog sinks and drains and send terrible odors into the home. This is why septic pump is very essential.

  46. Thank you for the great page of information. I’m interested in a 125′ x 125′ cottage lot, but neighbours have commented that no one would be able to build on it because of the size. Would I have to use a holding tank instead of a septic system in order to get both a well and sewage treatment for a future cottage to use? Thanks in advance!

  47. I had a septic installed and inspected. The installer forgot to place the barrier paper above the rock filter before he backfilled. The inspector passed this. According to Ontario building code the barrier paper
    is a very important part … without it the life of the septic bed can be reduced. Both the installation and inspection was negligent. Should I be concerned over the missing paper ? Or can I get away without otherwise I’m looking at a lawsuit. It’s only me at this house but who’s to say I won’t sell in the future.

  48. I have a 800 imp gal septic tank at my cottage. It was installed in 1979 and we’ve had no issues. As a matter of fact it’s been under used we were told because we are only there on weekends during the summer. I now want to replace the cottage with 1200 sq ft – 3 bedrooms and the town has informed me that the existing septic bed is not large enough to accommodate the new cottage. This came as a surprise as the leaching bed has 300 lineal feet of 3 inch pipe. What do you suggest?

  49. Thanks for the reminder that it’s important to have measures against flooding when planning to get a septic system installation service. I’d like to know more about how to find a good service like that because I’m thinking about buying a small rural property outside of the city. Being able to build my dream home there will surely require a lot of planning.

    • I was wondering if you were able to get the info you were looking for. I’m also interested in rural land that used to be a community center but closed for septic issues they couldn’t afford to repair. Did you find out anything?

  50. Distance between septic bed and in ground cistern?

  51. Thanks for sharing this informative article on septic systems in Ontario. As a homeowner, it’s important to have a basic understanding of how septic systems work and how to properly maintain them to avoid any issues down the line. This article provides valuable information and tips that are useful for any homeowner in Ontario. Keep up the good work!

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