Suitably engineered graphene-based materials could potentially be used to make water-separation membranes for applications such as desalination. Graphene-based materials with water-permeable pores can be made by creating either nanopores in graphene monolayers (see the figure, top) (1, 2) or two-dimensional (2D) channels that form between nanosheets of graphene oxide (GO) (see the figure, middle) (3). Both approaches face challenges for scaling to practical membrane sizes on the meter scale. The former requires creating a high density of subnanometer pores (4) on a defect-free monolayer graphene sheet that has high out-of-plane mechanical strength (5), and materials meeting all these requirements have largely been limited to micrometer-scale lateral dimensions. On page 1057 of this issue, Yang et al. (6) report production of nanoporous graphene on the centimeter scale that can reject between 85 and 97% of the salt from saltwater.