Scotch Guard, Camp Dry, others of different name will get you decent water repellency. They will however wash out. Reapplying is not a problem, but becomes time consuming and somewhat expensive. I have tried using other peoples "rejuvinating" waxes on an old hunting jacket, it didn't work. If you really want it water repellant. Hang it on the north side of a building so the sun does not hit it and paint it with boiled linseed oil. Takes a long time to dry and really should have a second coat but when your done, you chould have as near waterproof as you can get with cotton. One other option I can think of is using "Canvac" its used to recoat tents. I'm not sure of the spelling but that's close. Should be able to find it on line or places selling quality canvas tents.