JB Weld is great stuff. They also have a product called Waterweld which will set even when applied under water, but since you can dry out your can before making the repair, that's probably not necessary.

Gorilla Glue is also super and you'll find plenty of other uses for it around the house.

Any other epoxy product will work, but epoxy requires mixing and can be a pain to use.

A couple tips:

Clean the area thoroughly. Take a bit of sandpaper, steel wool, or even that pot scrubber thingy from your kitchen and rough up the surface around the hole. This will help the adhesive stick. Note, though, that if your watering can is galvanized, you don't want to scratch off the zinc coating except where the adhesive is going to go, or it will rust.

Read the instructions for the adhesive, particularly about "cure" time. Wait at least the specified time--or even twice that long--before you use the can.

Good luck.

Thank you, Pianojuggler. I will give it a try.

I'd second that JB weld.

Either that or a bit of that black pond foam that swells. It's tough stuff.

A bit too spendy to buy a can for a small application.

I used gorilla glue to plug the hole and to treat some areas that were ready to develop holes. Then I sprayed the whole bottom with primer so that it wouldn't develop rust where I sanded it. I think it will last me a long time now. Thanks!