If AI does all the work, then the cost of everything drops down to energy cost. And if robots are generating energy (via solar power or whatever) then that's free too.
That means it won't cost any human labor to provide food, water, even medicine. It will be effectively free. You might say, "but the people who own the robots will charge money." But why? What do the people who own robots need money for? And remember that if we're assuming all jobs are gone, robots are building other robots. The government (or even a philanthropic rich person) could just give everyone a robot (or two or ten).
There will still be an economy, because people will charge each other for unique, human-specific art/services/whatever. But that money will only be spent on human art/services/whatever. You won't need money for anything robots can create.