During times of emergencies, such as power outages, for those people that plan to empty the water out of their toilet bowls and then place a garbage bag in the bottom to catch the refuge, this is not a good idea.
Sewer gases are methane gas, and therefore, are very deadly and explosive .
News stories report that utility workers have died from exposure to methane gas. It is also important to add water to your floor drains or other unused drains about once a month in case the water has evaporated. If the sewer systems don't work, sewage can start to come up through the shower, tub, toilets, and even sink drains. This can also happen because of flooding, frozen drain pipes, blockages, etc. If one of these tips over and spills, you will have a major mess and most likely won't have enough spare water to clean it up.