Water main breaks can happen for many reasons. Freezing weather is a common cause as well as being struck by heavy equipment. If you see water running across the road or the sidewalk you need to report it to the water provider. If you have a water main break on your property it is your responsibility to do repairs.
When a break is reported plumbing crews are sent out to make sure it is a break and is on public property. After locating the leak they will dig it up and repair or replace it. Sometimes when the water line breaks the water to your home will be turned off during repair. After the repair you will want to run water for a few minutes to flush out any debris that may have gotten in the system.