There is 27,154 gallons of water in an acre inch. Two inches of water over 10 acres is 543,080 gallons. You need a lot of water. The amount of water you need for the season or per irrigation will depend on several things. The water holding capacity of your soil and the consumptive use of water by grass in your area are the two main ones. If you are sprinkler irrigating (either hand lines or a wheel line) you probably need at least 300 gallons per minute to affectively run the system. At 300 gallons per minute it would take a little over 30 hours of continous running to apply 2 inches of water to 10 acres. Do that... ballpark, once a week. Running a 20-30 hp pump 30 hours a week can expensive.