There are many reasons why you might receive a higher than usual water bill but the main reason would be an undetected water leak on your property.
Have you downloaded the EyeOnWater App yet? EyeOnWater.com
The EyeOnWater app will enable you to track your water usage at your residence daily. You will be able to monitor, and have a better understanding of how much water is being used during irrigation. Most importantly, having the ability to set up notifications on the app to inform you of an undetected leak on your property.