“Yes, we know it looks weird,” says Dan Black, admiring a sleek, curved water bottle containing what looks like . . . a giant black rock. But as with most gizmos from London-based design firm Black + Blum (whose Hot-Pot BBQ doubles as an herb garden), there’s more to the Eau Good bottle than one might expect: That dark mass is Binchotan charcoal, an über-porous substance much like the one Brita filters use to absorb nasty particles. “We want to present it in its natural form,” says Black. The challenge, then, was to design the rest of the capsule so well that people would embrace its avant-garde centerpiece–and stop buying bottled water, which generates millions of tons of plastic waste each year. Here’s how Black + Blum did it.
 Black and partner Martin Blum were inspired by the ruggedness of a military canteen, reflected in early prototypes. “We needed something you’d be proud to hold,” he says.
 “There’s a real science to spout size,” says Black. “Too big, the rim goes past your nose; too small, it’s tough to drink.” To determine the perfect diameter (3.8 centimeters), Black’s team spent weeks drinking from odd-shaped bottles. Among them: shampoo and bleach.
 Prototypes–shaped like liter bottles, not hourglasses–couldn’t support a squeeze-to-release mechanism for the charcoal filter (which should be boiled every few weeks). “We needed the whole thing to deform,” says Black.
 In lieu of a screw-top lid (which channeled a sports water bottle), the designers chose a simple cork with a silicon-coated underside.