The structure, dynamics, and properties of water are pretty well understood. We have a good idea of its structure, and how that structure explains why its properties are sometimes different from those of a ‘normal’ liquid. A number of issues remain, which suggest there may still be some things about water that we don’t yet understand. ‘Some past and current controversies’ considers the concepts of ‘memory’ of water; polywater (a form of water that was thought to be denser and more stable than ordinary water); and whether surface ordering impacts on the biological role of water. These have largely been resolved, but the idea of two possible liquid structures of water still remains.