If a leak is difficult to find, enlist a helper and go up on the roof with a garden hose. Start low, soaking the area just above where the leak appears in the house. Isolate areas when you run the hose. For example, soak the downhill side of a chimney first, then each side, then the top on both sides. Have your helper stay inside the house waiting for the drip to appear. Let the hose run for several minutes in one area before moving it up the roof a little farther. Tell your helper to yell when a drip becomes visible. You'll be in the neighborhood of the leak. This process can take well over an hour, so be patient and don't move the hose too soon. Buy your helper dinner. If running water doesn't reveal the exact location of the leak, don't be timid. Start removing shingles in the suspect area. With them removed, there'll be evidence of the leak and you'll be able to track it down right to the source. You'll see discolored felt paper or water-stained or even rotted wood directly below and around a leaky roof.