Every now and then, water pipes have a tendency to sprout little leaks that will require a plumber to service.  The difference in the cost of plumber service is whether or not the job is an emergency.  Small leaks can be handled as a non emergency; but, that means that the leak will continue until the plumber arrives which means further water damage until the plumber gets there.  A simple way to prevent further damage is to locate the leak via small inspection holes (water always travels downward) and use the inspection hole at the leak (extended to below the leak) to guide the water into a container or drain (sink or tub).  The way to guide the water is very simple.  Just tie a string tightly slightly below the leak, run it out the inspection hole (making sure the string runs downward as well as out), and away from the wall (over the outer end of the shower head for example if the leak is above the shower head or if there is nothing, use a nail angled downward and run the string over the head) and let hang.  The string will absorb the water and guide it to the lowest point of the string so long as the string has a downward angle where it can drip into a container below.  This will keep the water from doing further damage inside the wall and save an emergency call to the plumber.  Repairs will still have to be made from damage already done; but, there will be little further damage after the guide is put into place.  The minimizing of damage is especially essential with little hot water leaks because such leaks escalate mold buildup which is both a health hazard and expensive to clean up.  This is a method I have used several times when discovering a leak in between the upper condo unit and mine.