San Francisco led the movement to ban plastic shopping bags and is now proposing to ensure people have access to safe high-quality tap water and ban bottled water. A supporter of the ban says “The city is reinforcing water as a public good rather than a commodity that can be bought and sold by corporations.”

a. What is the externality that arises from drinking bottled water?

b. What methods other than a ban are available for dealing with the bottled-water externality?

c. Is it likely that banning bottled water is efficient?
Explain your answer.