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Watch out for contamination!

Drinking water is a precious natural resource. Its quality must be preserved.

As a building owner, you must ensure that your plumbing facilities are not in danger of contaminating the drinking water supply. The RBQ explains how contamination occurs and how to prevent it.

How does contamination take place?

When drinking water is in contact with a potential source of pollution, the phenomenon is called a cross connection. There are two types of cross connection, either through back siphonage or through counter-pressure:

  • Back siphonage produces backflow caused by a negative or subatmospheric pressure within a water distribution system. In diagram no. 1, a breach in the duct bringing water from the aqueduct causes a drop in pressure in the distribution system. The lack of protection for the basin results in dispersion of its contaminants into the water distribution system, leading to contaminated water coming out of a drinking fountain.
  • Counter-pressure can occur when a device or piece of equipment is operating on a pressure level above that of the drinking water distribution system. In the example opposite, a breach in the duct carrying water from the aqueduct causes a drop in pressure in the distribution system. Water containing chemicals from the heating system is under higher pressure than water in the distribution network and can contaminate the drinking water.

Measures must be taken to ensure effective protection from cross connections so as to prevent any drinking water contamination.

Diagram 1: Example of cross connection in a building
Diagram no. 1.

Preventing contamination

An air gap affords the best protection possible. This is an air space between the faucet and the overflow level of a fixture. In a lavatory, for instance, it is the air space between the faucet and the fixture's overflow level. This space must be sufficient to ensure that contaminated or dirty water overflowing the lavatory cannot get into the drinking water through the faucet (diagram no. 2).

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

Hooking a hose up to a valve, on the other hand, removes the air gap (diagram no. 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. A backflow preventer must be added for protection. Note that installing a single check valve does not make for effective protection; only backflow preventers approved in accordance with standard CSA B64.10 provide that degree of protection.

Contact a plumbing contractor holding a RBQ licence or take advantage of such a person's presence in your building to have a check done for possible cross connections and the required devices installed. Should the plumbing contractor also be an accredited inspector, do not let the occasion pass to have the building's devices checked for safety's sake.

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Avoid dramatic consequences

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. 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 hefty cleanup costs.

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

Field testing and maintenance of backflow preventers must be carried out by accredited personnel listed on the website of Réseau Environnement : vdar.reseau-environnement.comThis link open an external website of the Régie du bâtiment du Québec in a new window.. All the requirements for the selection and testing of backflow preventers are set out in standard CSA B64.10.

The RBQ reminds you that, as a building owner, you have an obligation to protect the drinking water system from contamination through cross connections by using adequate backflow preventers. You must have the devices verified at the time of their installation then annually and keep a record proving that verifications were carried out.

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