Water molecules bind to each other through covalent bonds, which are relatively weak but maintain some structure that varies with temperature.

“So when you have individual water molecules, they have the opportunity to interact and essentially bind to one another and they bind through what are called covalent bonds. Covalent bonds are relatively weak bonds, and so as a consequence, water can change its confirmation. However, covalent bonds are strong enough that water actually can maintain some structure and that structure will vary, of course, depending on its temperature.”