Hi Jess
If you really want to use the canteen to hold water when your on the field you will probably have to soak it in water so as to make it water tight again .
So fill the canteen with a mild solution of bleach & water and just let it sit .
This will swell the wood seams of the canteen and make it water tight again as well as killing any Krusty germs that may still be living inside the container . Lets face it Krusty is still alive so there maybe some of him still inside the canteen
After you have let it sit for 2 or 3 days rinse it out really good to get rid of the bleech taist .
Then you should be all set .
You will have to keep putting water in it so that the wood doesn't dry out again
which will allow the seams to shrink again .
Capt Dave