According to Quebec's ministère du Développement durable, de l'Environnement et de la Lutte contre les changements climatiques, private well owners must take special precautions when there is a flood because such events can present serious risks to the quality of underground water, which can be contaminated not only by river water but also by nearby septic systems. In order to avoid the risk of illness due to the consumption of contaminated water, the ministère recommends that those owners take the following steps.
Water from any well in a flooded area should be treated as unsafe to consume, and anyone who is affected should get their drinking water from another source (for instance from a neighbour who was not affected, a water distribution network or bottled water), or boil for one minute any water they intend to consume as drinking water or to prepare uncooked food.
Once the flood water has finally receded, owners should first check that their well equipment is intact, particularly the electrical circuit, and should then wait at least ten days before disinfecting the well in accordance with the procedure posted on the Web site of the ministère du Développement durable, de l'Environnement et de la Lutte contre les changements climatiques.
Once the disinfection procedure has been completed, the water will have to be analyzed.
After the disinfection, no fecal or coliform bacteria should be detected in the water samples analyzed.
If there are any such bacteria, the water must continue to be boiled. The well will have to be reinspected, and the disinfection repeated.
The results of both recommended series of analyses must indicate that the water is safe to consume.
Source: ministère du Développement durable, de l'Environnement et de la Lutte contre les changements climatiques du Québec.