You do have a water tank installed at your home don't you?  Well if you don't, get one, then get this nifty little wireless remote water level monitor from Rain Harvest.

The water sensor sits a-top your tank and uses ultrasonic radio waves, kind if like a fish finder I guess, to see how much water's in your tank.  It transmits a signal back to the receiver plugged in to a power-point in the home to give you a water level reading.