Repair a Broken Underground Water Line

A broken underground water line can be very costly and messy to repair. Here's a shortcut that has none of those disadvantages.

Steps

Determine where the water line is leaking. It's usually where the water is oozing to the surface.
Insert an air hose inside the line past the point of the break and apply air pressure to empty the line of remaining water.
Find a water line hose one size smaller than the broken water line. Insert it into the larger pipe and push it in, well past where the break is thought to be.
Keep pushing it into the pipe until the far end is submerged in water. You can tell by blowing into the smaller pipe and hearing bubbling.
In the space between the two pipes, inject an expanding urethane foam crack filler. The harder, less expanding type works best.
Hopefully, the urethane ran down to the water level, began to foam back up, sealed the crack, and you will see it oozing back out the top.
Clean up the excess foam, and wait for it to harden.
Connect the inner, smaller water line to the system and apply water pressure again.

Vertical water lines work the best. Horizontal lines do not.
If this method fails, you haven't lost much and you're simply back to the regular option of digging up and repairing the line.
Attaching a long, narrow tube to the urethane foam applicator helps to inject the foam more easily into the gap between the inner and outer pipes.
This method will not work unless the water line slopes downwards and away from you. You need the far end of the smaller, inner pipe to be submerged in water to prevent the foam from sealing the far end shut.

Urethane foam may or not be compatible with potable drinking water. This method is best for irrigation or stock watering applications.
If the underground water line is fairly horizontal, forget this method and dig it up instead.