How do I find a leak in a tube?

[oneboxermom]

Hi, my kids have their bikes apart to fix a flat but cannot find the leak in the tube to repair it. How can I find the leak and save money without buying a new tube? Thanks, Jenny

[DaveM]

Take out the tube, pump it up and see if you can hear the leak. If you can spot the general area, sometimes if you hold it close to your lips, you can feel the air leak better. If needed, put a few inches of water in a sink and hold the tube under the water. You should see a small stream of bubbles.
Make sure to feel along the inside of the tire to see if there is still anything sharp stuck in it. Otherwise, it can re-pop the tube after you put it back in.