Usually just a millimeter or so, but how dry is your climate? Around here, tomatoes need 5-10 gallons of water twice a week to stay happy. You may find yourself spending all day filling up cans!

Kevin : )

thank you, Kevin. We are not so dry here in PNW. I hope if i put two cans per tomato bush, it will let me to water plant by filling cans twice a week.
I'll try to make several holes and see how long it will take to drain whole can.