I used 10,000 gallons per acre, because we use 27,000 gallons per acre-inch, so watering an acre three times weekly to the nominal standard of an inch of watering gets you to a 10,000 gal tank to even supply one cycle of watering on an acre. Multiply by the number of acres, times the number of weeks worth of water you are trying to store, and you got one bigass storage tank.
