Drilling into a wall has the potential of causing serious and costly damage if a water pipe is accidentally penetrated. Taking the time to know where to drill does not take much skill and eliminates regrets later. It is possible to follow the water lines from the basement or crawl space to help determine the most likely path to sinks, tubs, toilets, radiators and washing machines. However, you won't know the exact location of the water lines in your walls until you use a pipe detector.
Purchase or rent a combination detector from a home improvement or plumbing supply store. Typically a combination detector will find studs, pipes and wires and will make a sound or flash a light when an item is detected.
Practice using the detector on a wall where you know the location of pipes, studs and wires. Listen for the different indicators and watch the flashing light while detecting each to learn the variations.
Find and mark the location of other water pipes in the walls once you are confident you can accurately interpret the pipe detector.