There are a number of things to investigate.
First, check to see if your meter reading is correct. The inside meter is usually located in the basement, crawl space, or utility closet for homes without a basement. The reading should be taken from left to right. The reading in thousands of gallons on your bill and the reading on the inside meter and should be close. (Remember to factor in the water usage since the reading date.) If the reading on your bill is higher, please call (847) 599-7500, describe the discrepancy, and someone will be dispatched to take a corrected reading.
Second, check for leaks in your home. An easy way to check for leaks is to read your meter either at night or when you will be away from home for an extended period of time. Read the meter again in the morning or when you return home, before using any water. If the reading has changed, this suggests a leak. Common areas to check for leaks are toilets, sinks, water softeners, humidifiers, and sprinkler systems. If you are unable or unsure how to repair a leak, contact a licensed plumber. Remember a leak means you are paying for water you are not using.