You obviously have a serious problem. I'm not a pro, and I won't even venture a guess at what you should do other than to explore all of the options, including finding and repairing the leak. If it is under the concrete patio, remember that concrete can be cut and repaired so the entire slab would not have to be removed. This being the start of the week-end, many of the plumber pros that frequent the forum may not see this post until next week, so keep checking back. I'm sure you will get some valuable pointers and suggestions from them. But you should know that the PVC that would be used for replacing the whole main line should that be required, comes in long rolls and is not the ridged kind of PVC in your lawn sprinkler system.