Last updated
Values this chapter turns on
- min first-flush diversion per area of roof
- 0.3 L/m²
- min first-flush diversion per area of roof
- max mesh of the debris screen ahead of the tank
- 6 mm
- max mesh of the debris screen ahead of the tank
- max filter mesh for indoor rainwater uses
- 50 μm
- max filter mesh for indoor rainwater uses
- min letter height on a non-potable water sign
- 25 mm
- min letter height on a non-potable water sign
Section 7.7. is short, but it is new ground compared with the House exam. It covers three things: general rules for any non-potable water system, rainwater harvesting systems, and systems that re-use water. Large commercial and institutional buildings are where these systems show up, so the All Buildings exam tests them. Most questions are lookups: which fixtures may receive non-potable water, where the pipes may not run, how they are marked, and the treatment train for harvested rainwater. There is one simple calculation, the first-flush volume.
Non-potable water systems in general
A non-potable water system must follow Subsection 7.7. and good engineering practice (OBC Div. B 7.7.1.1.OBC Div. B 7.7.1.1. General(1) Non-potable water systems shall be designed, fabricated and installed in accordance with this Subsection and good engineering practice. (See Note A-7.7.1.1.(1)) (2) Except as provided in Sentence (3) and Subsection 7.7.2., non-potable water systems shall only be used to supply water closets, urinals, trap seal…). The heart of the Article is a short list of permitted uses. Outside the rainwater rules of 7.7.2., non-potable water may supply only:
| Permitted use (general systems) | Note |
|---|---|
| Water closets | |
| Urinals | |
| Trap seal primers | |
| Underground irrigation | Directly connected, dispensing only below the ground surface |
Two hard limits follow. Non-potable water may never supply fixtures in healthcare facilities. And where a potable system tops up a non-potable one, the potable side is protected under 7.6.2.1.OBC Div. B 7.6.2.1. Connection of Systems(1) Connections to potable water systems shall be designed and installed so that non-potable water or substances that may render the water non-potable cannot enter the system. (2) Reserved. (3) Backflow preventers shall be selected and installed in conformance with CSA B64.10, "Selection and installation of backflow…, which brings in CSA B64.10 device selection. Static pressure above 550 kPa at a fixture calls for a pressure-reducing valve, the same limit as on the potable side. Where a clothes washer is fed by both a rainwater system and the potable system, the potable system gets dual check valve (DuC) protection for both area isolation and premise isolation.
Marking and location
Non-potable piping must carry permanent, distinct and easily recognized markings, and both piping and outlets are identified under CAN/CSA-B128.1 (7.7.1.2.OBC Div. B 7.7.1.2. Identification and Marking(0.1) Non-potable water piping shall be identified by markings that are permanent, distinct and easily recognized. (1) Non-potable water piping and outlets shall be identified and marked in accordance with CAN/CSA-B128.1, "Design and Installation of Non-Potable Water Systems." (2) A sign containing the words…). Above each fixture allowed to receive non-potable water, post a sign reading "non-potable WATER, DO NOT DRINK" in letters at least 25 mm high with a 5 mm stroke.
Location rules keep leaks away from anything people consume (7.7.1.3.OBC Div. B 7.7.1.3. Location of Pipes(1) Non-potable water piping shall not be located directly above (a) areas where food, drink or products that are intended for human consumption are prepared, handled, dispensed or stored, (b) a non-pressurized or pressurized potable water tank, or (c) food-handling equipment.). Non-potable piping may not run directly above:
- areas where food, drink or products for human consumption are prepared, handled, dispensed or stored,
- a potable water tank, pressurized or not, or
- food-handling equipment.
Outlets may not discharge into a sink or lavatory, into a fixture that also receives a potable outlet, or into a fixture used for food or drink preparation (7.7.1.4.OBC Div. B 7.7.1.4. Location of Outlets(1) Except as permitted in Sentence 7.1.5.3.(3), an outlet from a non-potable water system shall not be located where it can discharge into, (0.a) a sink or lavatory, (a) a fixture into which an outlet from a potable water system is discharged, or (b) a fixture that is used for a purpose related to the preparation…).
Rainwater harvesting
For Subsection 7.7.2., "rainwater" means storm water from an above-ground roof surface, and a harvesting system is the tank, pump, pipes and fittings used to collect and distribute it. A rain barrel that is not connected to the plumbing system is not a harvesting system (7.7.2.1.OBC Div. B 7.7.2.1. General(1) For the purposes of this Subsection, rainwater shall mean storm water discharged from an above-ground roof surface. (See Note A-7.7.2.1.(1)) (2) For the purposes of this Subsection, a non-potable rainwater harvesting system shall mean a storage tank, a pump, pipes, fittings and other plumbing appurtenances used to…). Note that the Division A definition of rainwater is wider (roof or ground, but not accessible patios and driveways); inside 7.7.2. the narrower roof-only meaning applies.
What harvested rainwater may supply
The rainwater list is longer than the general list (7.7.2.2.OBC Div. B 7.7.2.2. Permitted Applications(1) Non-potable rainwater harvesting systems are only permitted to supply (a) water closets and urinals, (b) clothes washers, (c) floor-mounted service sinks and laundry trays, (d) trap primers, (e) irrigation systems, (f) hydronic systems, (g) make-up water systems for heat rejection systems, or (h) any other…): water closets and urinals, clothes washers, floor-mounted service sinks and laundry trays, trap primers, irrigation, hydronic systems, make-up water for heat rejection systems, and any other use where the water is not expected to be ingested or inhaled. Lavatories and kitchen sinks are not on it.
Roofs and design
The roof that collects the water must be inaccessible to vehicles and pedestrians, and roofing and conveyance materials must not add substances that would harm the end use (7.7.2.3.OBC Div. B 7.7.2.3. Roof Design(1) Roof surfaces that supply rainwater to a non-potable rainwater harvesting system shall be inaccessible to vehicular and pedestrian traffic. (See Note A-7.7.2.3.(1)) (2) Roofing components and conveyance systems in contact with rainwater that is supplied to a non-potable rainwater harvesting system shall be…). A harvesting system may not collect discharge from an evaporative heat rejection system (a cooling tower, for example). Treatment must meet provincial requirements, or where there are none, the default treatment train in 7.7.2.4.(4)OBC Div. B 7.7.2.4. Non-Potable Rainwater Harvesting System Design(1) Non-potable rainwater harvesting systems and their connections shall be designed, fabricated and installed in accordance with this Subsection and good engineering practice. (See Note A-7.7.2.4.(1)) (2) Non-potable rainwater harvesting systems shall not collect water discharged from an evaporative heat rejection… applies, or treatment to the contaminant limits of CSA B805 / ICC 805.
| Default treatment component | Limit |
|---|---|
| Debris screen ahead of the tank inlet | Mesh not more than 6 mm |
| First-flush diversion ahead of the tank inlet | At least 0.3 L per m² of roof area |
| Calming inlet or settling chamber | Ahead of the tank inlet |
| Sediment entrainment protection | At the pump |
| Filter for indoor uses | Mesh not more than 50 μm, ahead of the tank inlet |
Tanks, overflow and make-up water
Storage tanks follow CAN/CSA-B126.0 and B126.1. Every tank has an overflow to a public storm sewer, public combined sewer, storm water management system or designated disposal location. Where the tank outlet is below the level of the adjoining street, the overflow must either use an indirect connection outside the building or have a backwater valve. The make-up water connection (potable water topping up the tank) needs either a reduced pressure principle backflow preventer or an air gap. Where a single fixture supply fitting mixes rainwater and potable water, the potable side needs a backflow preventer selected under 7.6.2.1.(3). As with other non-potable systems, a pressure-reducing valve is needed where static pressure at a fixture could exceed 550 kPa.
Systems for re-use purposes
Other re-use systems (for example greywater, which the Code defines as domestic sewage from fixtures other than sanitary units) follow good engineering practice such as the ASHRAE Handbooks, ASPE Data Books or CAN/CSA-B128.1 (7.7.3.1.OBC Div. B 7.7.3.1. Conformance to Standards(1) Except as provided in Article 7.7.2.4., non-potable water systems for re-use purposes shall be designed, constructed and installed to conform to good engineering practice appropriate to the circumstances such as described in (a) the ASHRAE Handbooks, (b) ASPE Data Books, or (c) CAN/CSA-B128.1, "Design and…). The Code gives no numeric design rules for them, so exam questions here ask which references apply.
Common traps
- Assuming non-potable water can feed a lavatory or kitchen sink. It cannot, under either list.
- Mixing up the two permitted-use lists. Clothes washers, service sinks and hydronic systems are on the rainwater list only.
- Forgetting that healthcare facilities are excluded entirely.
- Reading 50 μm as the screen size. The debris screen is 6 mm; 50 μm is the indoor-use filter.
- Treating a stand-alone rain barrel as a harvesting system.
Chapter review
Chapter at a glance
One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.
- Non-potable water systems in general
A non-potable water system must follow Subsection 7.7. and good engineering practice.
- Rainwater harvesting
For Subsection 7.7.2., "rainwater" means storm water from an above-ground roof surface, and a harvesting system is the tank, pump, pipes and fittings used to collect and…
- Systems for re-use purposes
Other re-use systems (for example greywater, which the Code defines as domestic sewage from fixtures other than sanitary units) follow good engineering practice such as the ASHRAE…
Usual exam traps
- Assuming non-potable water can feed a lavatory or kitchen sink. It cannot, under either list.
- Mixing up the two permitted-use lists. Clothes washers, service sinks and hydronic systems are on the rainwater list only.
- Forgetting that healthcare facilities are excluded entirely.
- Reading 50 μm as the screen size. The debris screen is 6 mm; 50 μm is the indoor-use filter.
- Treating a stand-alone rain barrel as a harvesting system.
Practice this chapter
Questions on Non-potable water systems (7.7), in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.
Code cited in this chapter
Based on the official 2024 Building Code Compendium on ontario.ca.
© King's Printer for Ontario, 2024. Reproduced with permission.
OBC Div. B 7.7.1.1. General
Open OBC Div. B 7.7.1.1. in the code viewer(1)Non-potable water systems shall be designed, fabricated and installed in accordance with this Subsection and good engineering practice. (See Note A-7.7.1.1.(1))
(2)Except as provided in Sentence (3) and Subsection 7.7.2., non-potable water systems shall only be used to supply water closets, urinals, trap seal primers, and directly connected underground irrigation systems that only dispense water below the surface of the ground.
(3)Non-potable water systems shall not be used to supply fixtures in healthcare facilities.
(4)Where a non-potable water system is supplied by a potable water system, the potable water system shall be protected in accordance with Article 7.6.2.1.
(5)Where the static pressure at any fixture in a non-potable water system may exceed 550 kPa, a pressure-reducing valve shall be installed to limit the maximum static pressure at the fixture to 550 kPa.
(6)Where a clothes washer is supplied by a rainwater system and a potable water system, the potable water system shall be protected by dual check valve backflow preventers conforming to CSA B64.6, "Dual check valve (DuC) backflow preventers" for
(a)area isolation, and
(b)premise isolation.
OBC Div. B 7.6.2.1. Connection of Systems
Open OBC Div. B 7.6.2.1. in the code viewer(1)Connections to potable water systems shall be designed and installed so that non-potable water or substances that may render the water non-potable cannot enter the system.
(2)Reserved.
(3)Backflow preventers shall be selected and installed in conformance with CSA B64.10, "Selection and installation of backflow preventers."
(3.1)No connection shall be made between a potable water system supplied with water from a drinking water system and any other potable water system without the consent of the water purveyor.
OBC Div. B 7.7.1.2. Identification and Marking
Open OBC Div. B 7.7.1.2. in the code viewer(0.1)Non-potable water piping shall be identified by markings that are permanent, distinct and easily recognized.
(1)Non-potable water piping and outlets shall be identified and marked in accordance with CAN/CSA-B128.1, "Design and Installation of Non-Potable Water Systems."
(2)A sign containing the words non-potable WATER, DO NOT DRINK shall be in letters at least 25 mm high with a 5 mm stroke and posted immediately above a fixture that is permitted to receive non-potable water.
OBC Div. B 7.7.1.3. Location of Pipes
Open OBC Div. B 7.7.1.3. in the code viewer(1)Non-potable water piping shall not be located directly above
(a)areas where food, drink or products that are intended for human consumption are prepared, handled, dispensed or stored,
(b)a non-pressurized or pressurized potable water tank, or
(c)food-handling equipment.
OBC Div. B 7.7.1.4. Location of Outlets
Open OBC Div. B 7.7.1.4. in the code viewer(1)Except as permitted in Sentence 7.1.5.3.(3), an outlet from a non-potable water system shall not be located where it can discharge into,
(0.a) a sink or lavatory,
(a)a fixture into which an outlet from a potable water system is discharged, or
(b)a fixture that is used for a purpose related to the preparation, handling or dispensing of food, drink or products that are intended for human consumption.
OBC Div. B 7.7.2.1. General
Open OBC Div. B 7.7.2.1. in the code viewer(1)For the purposes of this Subsection, rainwater shall mean storm water discharged from an above-ground roof surface. (See Note A-7.7.2.1.(1))
(2)For the purposes of this Subsection, a non-potable rainwater harvesting system shall mean a storage tank, a pump, pipes, fittings and other plumbing appurtenances used to collect and distribute rainwater, but shall not include a rain barrel not connected to a plumbing system.
OBC Div. B 7.7.2.2. Permitted Applications
Open OBC Div. B 7.7.2.2. in the code viewer(1)Non-potable rainwater harvesting systems are only permitted to supply
(a)water closets and urinals,
(b)clothes washers,
(c)floor-mounted service sinks and laundry trays,
(d)trap primers,
(e)irrigation systems,
(f)hydronic systems,
(g)make-up water systems for heat rejection systems, or
(h)any other application where the harvested rainwater is not expected to be ingested or inhaled.
OBC Div. B 7.7.2.3. Roof Design
Open OBC Div. B 7.7.2.3. in the code viewer(1)Roof surfaces that supply rainwater to a non-potable rainwater harvesting system shall be inaccessible to vehicular and pedestrian traffic. (See Note A-7.7.2.3.(1))
(2)Roofing components and conveyance systems in contact with rainwater that is supplied to a non-potable rainwater harvesting system shall be constructed of materials that will not introduce substances into the rainwater that could adversely affect its intended end use. (See Note A-7.7.2.3.(2))
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OBC Div. B 7.7.2.4. Non-Potable Rainwater Harvesting System Design
Open OBC Div. B 7.7.2.4. in the code viewer(1)Non-potable rainwater harvesting systems and their connections shall be designed, fabricated and installed in accordance with this Subsection and good engineering practice. (See Note A-7.7.2.4.(1))
(2)Non-potable rainwater harvesting systems shall not collect water discharged from an evaporative heat rejection system.
(3)Non-potable rainwater harvesting systems shall be provided with a means to treat the harvested rainwater in such a manner that the quality of the delivered non-potable water conforms to appropriate provincial or territorial requirements or, in the absence of such requirements, the systems shall conform to Sentence (4). (See Note A-7.7.2.4.(3) and (4))
(4)Except as provided in Sentence (3), non-potable rainwater harvesting systems shall be provided with
(a)a water treatment system consisting of
(i)a debris screen with a mesh size of not more than 6 mm ahead of the storage tank inlet,
(ii)a first-flush diversion system with a capacity of not less than 0.3 L/m² of roof area ahead of the storage tank inlet,
(iii)a calming inlet or settling chamber ahead of the storage tank inlet,
(iv)a device to prevent the entrainment of sediment into the pump, and
(v)where the harvested rainwater is used for an indoor application, a filter with a mesh size of not more than 50 μm ahead of the storage tank inlet, or
(b)a means to treat the harvested rainwater in such a manner that the delivered non-potable water contains not more than the maximum acceptable levels of contaminants stated in CSA B805 / ICC 805, "Rainwater harvesting systems." (See Note A-7.7.2.2.(1) and 7.7.2.4.(3) and (4))
(5)Where the static pressure at any fixture in a non-potable rainwater harvesting system may exceed 550 kPa, a pressure-reducing valve shall be installed to limit the maximum static pressure at the fixture to 550 kPa.
(6)Storage tanks in non-potable rainwater harvesting systems shall be designed and installed in accordance with
(a)CAN/CSA-B126.0, "General requirements and methods of testing for water cisterns," and
(b)CAN/CSA-B126.1, "Installation of water cisterns."
(7)Storage tanks in non-potable rainwater harvesting systems shall be equipped with an overflow that directs excess rainwater to
(a)a public storm sewer,
(b)a public combined sewer,
(c)a storm water management system, or
(d)a designated storm water disposal location.
(8)Where the storage tank outlet is located below the level of the adjoining street, the storage tank overflow required by Sentence (7) shall
(a)with an indirect connection that is not located within the building, or
(b)be equipped with a backwater valve.
(9)Make-up water connections to non-potable rainwater harvesting systems shall
(a)be equipped with a reduced pressure principle backflow preventer, or
(b)have an air gap.
(10)Where a fixture combines water from a non-potable rainwater harvesting system and potable water at the fixture supply fitting, the potable water system shall be protected by a backflow preventer as described in Sentence 7.6.2.1.(3).
OBC Div. B 7.7.3.1. Conformance to Standards
Open OBC Div. B 7.7.3.1. in the code viewer(1)Except as provided in Article 7.7.2.4., non-potable water systems for re-use purposes shall be designed, constructed and installed to conform to good engineering practice appropriate to the circumstances such as described in
(a)the ASHRAE Handbooks,
(b)ASPE Data Books, or
(c)CAN/CSA-B128.1, "Design and Installation of Non-Potable Water Systems."