Using special channel geometries, the efficiency of water cooling of silicon crystals at room temperature can be improved to the point where it becomes very attractive for use with x-ray monochromators at high-power synchrotron radiation beamlines. Prototype monochromators using two different geometries have been built and tested. The microchannel geometry uses long, parallel channels approximately 50 μm in width. The pin-post geometry creates a two-dimensional network of submillimeter water passages. Both geometries have excellent thermal performance, though preparing strain-free crystal assemblies containing such small features remains problematic. When perfected, water cooling using microchannel or pin-post geometries should be particularly suited to monochromator crystals used at wiggler beamlines.