Watch out for contamination!

As a building owner, you have an obligation to protect the drinking water system from contamination by using adequate backflow preventers (DAr). You must have the devices verified at the time of their installation then annually and keep a record proving that verifications were carried out.

All the information contained in this page can also be found in the brochure Potable water system: Beware of contamination! [Fr] – PDF (1,1 MB) 

How to protect the potable water system and the municipality’s water system?

In order to protect the potable water system of your building or your municipality, you must install backflow preventers where there is a risk of contamination and at the water inlet of your building. You must also have these devices tested on an annual basis by a plumbing contractor.

How does contamination take place?

When drinking water is in contact with a potential source of pollution, it can lead to a cross connection. There are 2 types of cross connection:

  • Back siphonage, which produces backflow caused by a negative or subatmospheric pressure within a water distribution system
  • Back pressure, which can occur when a device or piece of equipment is operating on a pressure level above that of the drinking water distribution system.
Diagram 1: Example of cross connection in a building
Diagram no. 1.

In diagram no. 1, a breach in the duct bringing water from the aqueduct causes a drop in pressure in the distribution system, and the 2 types of cross connection. Thus, the lack of protection for the basin results in dispersion of its contaminants into the water distribution system. Consequently, someone is drinking contaminated water from a drinking fountain – it’s the back siphonage. Moreover, water containing chemicals from the heating system is under higher pressure than water in the distribution network and can contaminate the drinking water – that’s back pressure.

How to prevent contamination?

The best possible protection is an air-gap separation, which is an air space between the valve and the flood level of the appliance. For example, in a sink, it is the air space between the faucet and the flood level of the sink. This space is great enough that dirty or contaminated water that could flood out of the sink cannot contaminate the potable water from the faucet (Diagram 2).

Diagram 2: Example of an air-gap separation
Diagram no. 2.

However, hooking a hose up to a valve removes the air gap (Diagram 3).

Diagram 3: Example of a frequent cross connection
Diagram no. 3.

A cross connection then becomes possible and, through back siphonage, infectious could infiltrate the drinking water distribution system. The solution: installing backflow preventers in places at risk and at the water inlet of your building in order to protect the municipality’s water system or your wells. 

Potable water? Protect it!

Note that installing a single check valve does not make for effective protection; only backflow preventers approved in accordance with standard CSA B64 and installed in accordance with standard CSA B64-10 provide that degree of protection. Chapter III, Plumbing, of the Construction Code and Chapter I, Plumbing, of the Safety Code refer to these standards.

Hire a professional

Contact a plumbing contractor holding a RBQ licence or take advantage of their presence in your building to have a check done for possible cross connections and the required devices installed. To find a licenced contractor, use the Licence holders’ repertory.

Should the plumbing contractor also be a certified inspector, do not let the occasion pass to have the building's devices checked for safety's sake.

All the requirements for the selection and testing of backflow preventers are set out in standard CSA B64.10. The field testing and maintenance of backflow preventers must be carried out by a certified inspector. The list of these inspectors is available on Réseau Environnement’s websiteThis link open an external website of the Régie du bâtiment du Québec in a new window..

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Why protect potable water system?

Drinking water is a precious natural resource, and its quality must be preserved. An inadequate installation in your building could cause the contamination of your well water or your municipality's drinking water supply, with potentially disastrous health consequences. Indeed, drinking contaminated water can cause stomach ache, diarrhea, skin blisters and even death.

Were it proved that the contamination of the drinking water distribution system originated from your building, you could be charged with a criminal act and have to pay cleanup costs of your municipality’s water system.

Prevention is your best ally! None of this will happen if you fulfill your obligations in the matter.

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