Power outages mean no running water, which leads to no flushing of toilets, and without heat, there is the added threat of pipes freezing and bursting.
To prevent pipes from freezing it is a good idea to drain the pipes and shut off the main water supply. Before you drain your pipes you may first want to collect water in clean containers for emergency drinking and cleaning purposes.
Open all faucets, including your water heater. If you have an electric hot water heater, drain the hot water heating system by turning it off and leaving the valves open.
Add plumbing antifreeze or recreational vehicle winterizing solution to the toilet and other pipes and traps with standing water.
If you have a septic tank, antifreeze could damage it so make sure you pump the chemical from the plumbing fixtures and pipes before they are refilled with water. Do not drink water you have added anti-freeze to!
If you have no running water and wish to continue to use your toilet, fill your bathtub with snow or water from a creek. After using the toilet pour a bucket of water in the toilet and it will flush automatically.
If your pipes do freeze, do not attempt to thaw them yourself. Contact a qualified professional. Many people set fire to their houses attempting to thaw water pipes themselves.
If your basement is flooding and you have no emergency generator to power a sump pump or other means to pump the basement, move all furniture and anything of value to a dry location and disconnect the power supply to prevent damage when the power comes back on.