The size of the area you can spray depends entirely on the amount of water penetration you need into the ground. For a 1000 square ft area at 1/8th inches of ground water penetration you need around 78 gallons of water. For a 1000 square ft area at 6-8 inches of groundwater penetration you need at least 620 gallons of water. This is roughly 1 inch of water per square foot or .62 gallons per square foot.