We live in the age of artisanal everything, from chocolate and coffee, to, you guessed it, water. At Mexico City's Casa del Agua, staff produce and bottle "local water" on-site. The bottles—designed artisanally, of course—are charming souvenirs that you can use over and over again (with your own, less expensive water) once you're home. Be sure to go to the second level of the shop to see the filtration process, and to the terrace level to see where the water is captured.
Yes, it's a bit precious, this idea of going to a bar to drink locally-made . . . water. But reserve judgment until you visit Casa del Agua, where the staff turns rainwater into drinkable water via a triple filtration system. That system is visible to all visitors: rainwater is caught on the roof and then helped by gravity to cascade through the filtration system, which is the centerpiece of the casa. It's an impressive one, too. Buy your own bottle of agua (all water comes in locally designed glass bottles that you can take with you and reuse--a great souvenir) and head to the roof for a drink.