Assuming that you’ve located the site of the leak, and it’s not a water main but a pipe on the meter side of your house, the DIY option would be to dig a trench around the leak, repair the pipe, refill the hole, and patch the damage to your landscape.
While fairly straightforward, it certainly won’t be easy (or clean) work.
If you don’t want to disturb your landscape, can’t find the source of the leak, or if the leak is in an inaccessible spot such as under a driveway, you may want to consider calling for reinforcements.
Some plumbing contractors offer “trenchless” underground pipe repair involving resins and patches that can be inserted on the pipe from one end then moved into place.
If you decide to repair the leak yourself, keep these tips in mind:
Plan ahead: If this is the main supply line to your house, you’ll have to keep your water turned off while repairs are underway.
Building codes: Find out the current building codes regarding underground plumbing and get advice about the type of repair materials that work best and resist corrosion in your soil.
Buried utility lines: Call 811 and have the utility companies come out and mark the location of any underground gas lines, electrical wires, and other buried cables before you start digging!
Prepare for the worst: The pipe may be deteriorated and have to be replaced entirely.
While you may not want to tackle that big a job, the time spent diagnosing the situation will save you time and money in the long run.
Digging: Make the trench large enough to access at least a foot of pipe on each side of the leak and a foot underneath it.
You need room to work, and you need to be able to inspect the area to find out what may have caused the leak.
Work carefully and slowly, making sure you don’t make the problem worse by hitting the pipe with a shovel.
Repairing Pipe: Once you’ve uncovered the pipe, measure the outside diameter and determine the type (PVC, copper, steel, etc.).
You may even want to take a photo of it with you. Ask your local plumbing supply for help choosing the correct repair fittings.
A knowledgeable sales associate can help you walk away with exactly what you need, including instructions.
Careful preparation and the proper tools, can make the difference between a plumbing repair and a plumbing nightmare, but even the best planned jobs can hit snags, so give yourself plenty of time.