The most of watering cans I decorate are of small size, less than 3 litre capacity, more suitable for watering houseplants or to use in the conservatory or greenhouse. But sometimes I work with a watering can of proper size!
This is proper 9 litre watering can for a garden. The only problem is that if it's left outside for a too long time especially in cold and rainy weather the decoration could be damaged. I put a lot of effort in protecting it with many layers of hard wearing varnish and still I warn castomers not to leave it outside after use.