This sounds like an emergency situation, a broken main, versus someone digging. These get discovered when Joe schmo turns his water on and it’s brown, no pressure, or someone driving down the street encounters a flood on a sunny day. They contact the water company, and the water company then identifies the problem. Time is continuing to pass as this all occurs.

Water utility calls every account holder affected by the outage. They post online. They notify the town and the town posts on their website. Dunno what this “system no one knows about” is, but around me there’s a service called Nixle that I use, and you’ll get text messages about things, including water main breaks and boil water advisories.