If you're self-employed, you advertise well, and do consistently good work, then you may not need any other qualifications. If looking to be hired, however, you'll likely have to be enrolled in an apprenticeship program. During this time, you will receive several years of paid, on-the-job training and access to classroom instruction in such subjects as math, drafting, applied physics and chemistry, and plumbing codes and regulations. You will also need to pass a plumbers exam and, depending on where you are working, become licensed by the state. And you thought all you needed was a wrench and a bit of elbow grease.