There's nothing as frustrating as curling up with a hot water bottle on a cold day, only to feel a wet patch forming on your clothes. A leaky hot water bottle will do you no good but, fortunately, with the proper supplies, you can repair it. Some hot water bottles may come with repair kits while others may require the purchase of some basic supplies.
Fill the hot water bottle and apply gentle pressure to find the leak. Observe the location where the water is coming from and mark the spot with a permanent marker.
Dry the hot water bottle. Hang it up in a spot to allow it to air dry for at least 48 hours, with the cap removed, to ensure the interior is moisture free.
Cut a piece of the patch material that came with the hot water bottle or cut a patch from a bicycle tire inner tube repair kit. Make sure the patch is large enough to cover the entire leak along with the perimeter around the leak.
Apply a thin layer of rubber cement over the area of the leak. Spread it as thin as possible. Apply a thin layer to the back of the rubber patch as well. Allow the glue to partially dry.
Press the patch over the area of the leak and smooth it over with your hand. The goal is for the patch to be as flat as possible. Allow the patch to dry overnight before using the hot water bottle.
This method works best for small holes. With larger holes, purchasing a new hot water bottle is a better solution.