Straight from the Health Canada website:

“Typically in the North, surface water is naturally clean and safe to drink. However, lake water or melted ice water (surface water) can become contaminated. Even the water from your water tank can become contaminated if it is not maintained adequately.

What are the possible health effects?

Health effects that come from drinking contaminated water include:

• Gastro-intestinal infections
• Nausea and vomiting

Tips – What can you do?

• The owner of the house should ensure that water tanks are cleaned and disinfected when the tank is first installed and once a year thereafter. You should never try to enter the water tank. Water tanks are dangerous because they are confined spaces and may not contain or allow in enough air to breathe”…