How do I fix a leaky pipe under the sink?

First place a bucket under the leak and shut off the water supply. Tighten any loose slip nuts or compression fittings by hand or with gentle wrench pressure. If the leak is from a cracked pipe, use a pipe repair clamp or epoxy putty as a temporary fix. For leaking at threaded connections, apply plumber's tape to the threads before reassembling. Replace corroded metal pipes with PVC or braided supply lines if needed.