Ugh, cast iron (and galvanized steel). It happens. A couple years ago at work a 4 inch pipe burst over a 3 day weekend. That pipe was about 35 years old. Nobody noticed (or cared to report it) as it flooded 4 feet high and poured out into the street for days.
There is a company I know of - a stockbroker friend pitched their stock to me years ago - that makes rubber sleeve inserts on a scale for municipal use. This is a problem across the country - old water mains and sewers that crack and break, and very expensive to repair and rebuild. Much cheaper to be pro-active and go in and line these pipes with a rubber coating. I didn’t buy the stock. It may be doing well, but my hunch is cities and states aren’t that big into the “maintenance and prevention” business the way a private property owner would be. They just wait until it breaks and charge it to the taxpayers.
Water companies practice what I call “Whack-a-mole” maintenance ie: “When a leak shows up - fix it”. We don’t have any dollars to replace that failing water line system.
The plastic liner is possible fix and is used successfully for sewer systems.