I never thought about intentionally leaving water out for wasps, LOL but I do keep one shallow plant saucer on the ground by the fence for the Carolina Wrens, and I have seen wasps around it on occasion. We have the Paper Wasps here in Florida and I remember being stung by one a couple of years ago ... the sting was a bit painful!
More interesting facts about the Paper Wasp:
http://www.floridabugs.com/Flo... In that link it mentions that they feed on ripe fruit so I guess that's why I see them around at ground level beneath my neighbors fruit trees every year, they must be feeding on the over-ripe fruit that's occasionally on the ground.
