“First things first: Call a plumber immediately if you have a leak, no matter how small. People often assume that little drips will stop on their own, but most get worse. And when water seeps into your walls or damages your floors, the repair can run up to several thousand dollars. If you have a number of nonurgent issues besides the leak, like a slow-draining sink or a faucet that needs to be installed, ask that all the repairs be made in one visit; your bill could be up to 25 percent lower than if the plumber makes multiple visits. And tell him if a family member or a friend referred him. He may do a small fix gratis, which he wouldn’t do for a cold-call customer.