It might be small. You might not even notice it's there. But a pipe joint is a vital connection that ensures a tight and very necessary seal in your pipe. Obviously, such important components are designed to be durable. Despite the sturdiness of these parts, however, they sometimes develop leaks.
If you have a soldered copper pipe joint and notice it leaking, you'll definitely want to re-solder it. But rest assured, a little epoxy on the trouble area is a good temporary fix. Here's a simple way to get the job done:
Clean the joint well with sand paper.
Be sure the joint is dry, then apply epoxy securely around the whole joint.
Wait for the epoxy to cure before running water through the pipes again.
If your leaky joint is in threaded iron pipes, your best bet is tightening the pipe or fitting, using specialized pipe wrenches. Bear in mind that sometimes pipes must be taken apart or possibly cut before they can be tightened. In this case, you might want to try applying epoxy to the leaky joint. Hopefully, this will solve the problem. If not, it's likely the leaky area of the pipe will need to be replaced.