Greywater Pit in Ontario: When a Class 2 System Is Legal

What a Greywater Pit Is (and What It Is Not)

A greywater pit is the oldest trick at the Ontario cottage: a covered hole in the ground, lined with something open-jointed, that soaks up the water from your sinks, shower and laundry. In Building Code language it is a Class 2 sewage system, and yes, it can be completely legal.

It can also be the single most common reason an old cottage gets a deficiency letter. The difference between those two outcomes is about four rules, a flow limit, and whether anybody ever hooked a toilet to it.

The one rule that never bends: a greywater pit takes greywater only. The Code says a Class 2 system “shall be designed only for the treatment and disposal of greywater.” Greywater is water from kitchen sinks, tubs, showers, washing machines and laundry tubs. Anything with human waste in it is not greywater, no matter how clean the toilet looks.

The Five Classes of Sewage System in Ontario

Ontario sorts every sewage system into one of five classes under Part 8 of the Building Code (Article 8.1.2.1). Knowing which one you have tells you which rules apply.

The pairing that matters for cottages is Class 1 plus Class 2: an outhouse or composting toilet for the human waste, and a greywater pit for the dishwater and shower. The Code keeps them separate on purpose. A Class 1 system is designed to receive only human body waste, and if it has a drain for excess liquid, that drain has to go to a Class 3, 4 or 5 system — not to the greywater pit (Tay Valley Class 1 guideline).

When Is a Greywater Pit Legal?

Here is the checklist we would run before anybody picks up a shovel. Miss one and the pit is either illegal or about to fail.

1. Greywater only. No toilet, no urinal, no composting-toilet leachate.
2. Under 1,000 L a day. A pit is only allowed where the daily design flow is less than 1,000 litres (North Bay-Mattawa CA Class 2 sheet).
3. At least 900 mm above the high groundwater table. Thunder Bay District Health Unit applies the same 900 mm to bedrock.
4. Surrounded by 600 mm of decent soil. At least 600 mm on all sides and below, with a percolation time under 50 minutes.
5. A permit. A Class 2 system treats and disperses sewage, so it is inspected and approved under the Building Code. Your township, health unit or conservation authority issues it.

Note what is not on the list: running water. The Code allows a pit with pressurized water. It just counts the flow higher, and that is where most cottages hit the wall.

Greywater Pit Sizing: The Two Numbers That Decide Everything

Sizing starts with flow. The Code counts fixture units and multiplies: 200 L per fixture unit with pressurized water, 125 L per fixture unit without it (Article 8.4.1.2). Kingston’s Class 2 form lists a tub or shower, clothes washer, laundry tub and each sink at 1.5 fixture units, and a dishwasher at 0.5 (City of Kingston Class 2 form).

Now watch how fast pressure eats your budget:

So a hand-pump cottage can run four fixtures into a pit. The same cottage with a pressure tank and a bathroom vanity is over the limit and needs a different system. Thunder Bay District Health Unit goes further and recommends a pit only where there is no pressurized water at all.

The second number is the soil. The pit is sized on its sidewall area, not its volume. The loading rate is LR = 400 ÷ T, where T is the soil’s percolation time in min/cm, and the required sidewall area is the daily flow divided by LR. The North Bay-Mattawa sheet works an example: 900 L/day in T = 10 soil gives LR = 40, so you need 22.5 m² of sidewall. A pit 1.0 m deep, 5.5 m long and 6.0 m wide gives 23.0 m².

Run the same formula on the hand-pump sauna (sink plus shower drain, 375 L/day) in the same soil and you need about 9.4 m². A pit 1.0 m deep and 2.4 m square gives 9.6 m². That is a worked illustration, not your design. Your T-time comes from a soil test, and our T-time guide explains how it is measured.

How It Has to Be Built

Article 8.4.2.1 is short, and every line of it is something an inspector can see:

Clearances for a greywater system are shorter than for a leaching bed, but they are not zero. Leeds and the Thousand Islands publishes this summary for Class 1 privy vaults, pail privies and Class 2 greywater systems (source):

Those are minimums. Thunder Bay’s guide uses 15 m to any watercourse, and many lake townships add a zoning setback on top (Leeds and the Thousand Islands notes a 30 m watercourse setback in its zoning by-law). On a waterfront lot, the zoning number usually wins. Our setback guide and waterfront septic guide cover the rest.

Where Greywater Pits Fail at Re-Inspection

Re-inspection programs go looking for exactly this. Tiny lists “deficient grey water disposal” among the things its inspectors check. Dysart lists “greywater to grade” as a remedial action. Innisfil calls out outhouses in disrepair. Here is what that looks like on the ground:

1. The pipe to nowhere. The sink or outdoor shower drains straight onto the ground or the rocks. That is not a Class 2 system. That is a fail.
2. The sauna drain to the lake. Shower water from a sauna is greywater. Running it down the shoreline rocks is the fastest way to meet the inspector.
3. No cover, or a rotten one. An open pit is a safety problem and a Code problem.
4. The collapsed barrel. Rusted-out steel drums fill with soil and quit soaking up water. You see it as a wet spot that never dries.
5. Too close. Pits dug in the 1960s at the water’s edge, or beside the dug well.
6. The upgrade nobody permitted. A pressure system and a bathroom vanity added later, so the old pit is now taking more than 1,000 L a day.
7. A toilet on the line. Somebody plumbed a flush toilet into it. This is not a deficiency, it is a new system.

The fix for 1 to 5 is usually a properly built, permitted pit in the right spot. The fix for 6 and 7 is a different system type altogether. If you are planning a bunkie or sleep cabin, read our bunkie septic guide before you run a sink to it.

Sources: OBC 8.1.2.1 (buildingcode.online), North Bay-Mattawa CA Class 2 sheet, Thunder Bay District Health Unit Class 2 guide, City of Kingston Class 2 form, Leeds and the Thousand Islands clearances, Tay Valley Class 1 guideline. Final approval belongs to your local building department, health unit or approval authority.