The arrangement of water molecules in the liquid state. Unlike the case of ideal gas (random distribution) and ideal crystal (perfect order) models, there is no simple way to describe the ideal liquid water structure. It is known that the structure has short range order (similar to ice) but no long range order (similar to a gas), as shown by x- ray diffraction studies. Several competing models exist that attempt to explain the observed properties of water. Examples include the quasi-crystalline model, which assumes that water consists of broken-down pieces of ice; the clathrate model, which suggests that water resembles the clathrate structure of gas hydrates; and the bend-bond model, which suggests that the bonds are bent to various degrees. Other models also exist. Water has several properties of direct meteorological interest (e.g., maximum density at +4°C; maximum visible refractive index at +1°C; maximum thermal capacity at +35°C; large static dielectric constant (80) and its frequency variation) with which such models need to be consistent.