If you are on a water well and experience a power failure, the pressure switch may be of the type that has to be reset. If you have used water during the time while the power was off and now your water won't come on that may be the problem.
When you have a power failure and continue to use water, the pressure switch, which has a gray plastic cover and is located near your well's pressure tank, will have to be reset. What happens is that when the pressure tank pressure falls below the low setting, usually between 20 and 35 psi, it causes the pressure switch to turn off.
First, after power is restored, check the well's main breaker, which should still be on. If it is tripped then inspect the well and wiring for any sign of a short before flipping the breaker on. Sometimes power fluctuations just before an outage will cause it to trip if the pump happens to be on during that time.
Locate the pressure switch. It will be approximately 3 inches long by two inches wide, two inches high and will be connected to a 1/4 inch metal pipe sticking up from the main water line coming from the well going to the pressure tank. It will have wires coming out of it going to the pump and to the breaker box. On the side of the gray pressure switch you will most likely see, toward the bottom, a shiny lever about an inch or two long. Using your insulated pliers, in case of stray electrical current, lift the lever upward. You should hear the pump kick on. Hold this lever in the upward position until you notice the pressure gauge get up to above 30 or so. Now if you turn it loose the pump should stay on and you are back in business.
Note that not all pressure switches have this lever and this method does not apply to them.
Non power outage problems related to all pressure switches include corrosion of the contacts and fire ants getting into the contacts. NEVER remove the cover of the switch without turning off the breaker and letting anyone that may turn that breaker back on know what you are doing. If you have to clean these contacts, after disconnecting the power use spray contact cleaner and a small brass brush. Use a screwdriver to tighten electrical connections if necessary.