Consider replacing the flapper and inspect the inside of the tank to see if there is any build-up preventing a proper seal. Also inspect the lift wire/guide to see if it is bent, corroded or catching on something, preventing the flapper from closing properly.
The float arm needs to be adjusted so that the water level is 2" below the top of the overflow pipe. The float arm may need to be repositioned to obtain the desired water level. If it is a plastic float arm, adjust the screw located at the top of the arm. Also make sure the refill tube is located about 1/4" over the overflow pipe. If necessary, clip the tube to the overflow pipe to stabilize it and keep it from moving into the overflow pipe.
Consider replacing or repairing the service line to prevent larger loss of water. A professional service may need to be contacted for completing this task.
At this point, try to determine where the water is going inside the home.
Finally, if all of the above tests show no evidence of leaked water, check the appliances that cycle. Water softeners can cause an increase in usage, so check the settings to make sure it is not cycling more often than necessary and monitor its full cycle to make sure it is operating properly. Also check outside spigots and hydrants to make sure they are not dripping, especially when connected to a sprinkler, soaker hose, or irrigation system. Take note of the times when extra water may be used, possibly weekends and evenings, when watering plants and gardens.
Check out our Conservation Tips under News & Notices for more suggestions.