Minecraft wiki entry for Ice_farming, associated text: Ice could theoretically be generated in the same way as cobblestone using two water source blocks, even to the extent that it could be piston-driven and used to build self-repairing structures. However, ice freezes slowly enough that an absurdly long clock cycle or a BUD (Block Update Detector), such as an observer, would be needed. Either way, it would serve as a very impractical toy. You can also make it high in the air to freeze the water.