If the leak is located before the meter, the city is responsible for the repair. This leak will not affect your consumption as it is not running through the meter.
If the leak is located after the meter, the homeowner is responsible for the repair. Sometimes, a simple repair can stop a costly leak.
Water usage determines the bill amount. Some of the most common reasons for increased usage are: leaking toilet (200 gallons per day!), broken underground irrigation drip line, broken sprinkler head. When a new home is purchased, the sprinklers are often set to water several times per week to set the sod. A good rule of thumb would be for new homeowners to lower usage to no more than 4 minutes at a time, twice per week, and adjust if needed. Similarly, always check your system after a power outage, which can reset the irrigation system to these high usage settings!