Contruction Errors
SERVPRO of Hyde Park / Central Austin works with a lot of local building contractors and plumbers. It is not uncommon for a home owner to find a water damage months or even years after a construction project or new home build. Most common error is a drywall screw that missed a stud in the wall and it penetrates a pipe.
Although I have seen nails too. The pipe is usually a drain line where the leak is slow and takes some time to discover. I have seen supply pressure lines with a nail and screw in it and still has taken years to for the leak to create enough water damage to be visible for the home owner to discover.