If you have well water and an electric-powered well pump (as most homes have), no. However, most water systems will retain a residual amount of water pressure even after the pump shuts off. You may be able to draw a few gallons of emergency water from the faucets.
If your house is prone to power outages, it might be a good idea to fill a bathtub or basin with water during electrical storms, just in case. Even better, a generator can keep your pump — and furnace — going during a power failure.