One common way a plumber will diagnose how bad your leak is by inserting an air tube into the pipe. The plumber will guide the pipes past the spot where the leak is and open the pressure valve. The air being forced into the pipe will actually help the plumber diagnose the severity of the leak by looking for tiny bubbles on the pipe.
If the leak is not severe, the plumber may offer to repair (or patch) the leaky pipe for you. This is usually quite cheaper than replacing the pipe. He can patch the pipe from within using an expanding urethane foam to seal the area. Or, your plumber can patch the pipe from the outside. An example of this would be clamping or soldering a metal pipe.
If the leak is bad enough to replace the pipe, your plumber will discuss options with you such as
Replacing the pipe with a metal pipe
Replacing the pipe with a plastic pipe
If you must have a pipe replaced in your home please make sure that your plumber is licensed and insured. You don’t want a catastrophe developing down the road because the plumber was not certified. Here where we live, a licensed plumber in the Melbourne, Florida area is affordable and will get the job done right.
The Sooner the Better
The sooner you get the pipe repaired or replaced the better. Even the tiniest of leaks can cause serious long-term damage. Think about how costly it can be to replace an entire ceiling on the floor below yours. Or, think about how much danger black mold imposes on you and yours. Having it done right the first time and in a timely manner is the only way to go.