The formation water density is defined as the mass of the formation water per unit volume of the formation water. Electronic densiometers can quickly determine the density with accuracy of / 0.00001 g/cm3 over a wide range of temperatures, although most oilfield data are reported at a 60 F reference temperature. In the past, density in metric units (g/cm3) was considered equal to specific gravity; therefore, for most engineering calculations, density and specific gravity were interchangeable in most of the older designs. However, process simulation software used in modern facility design uses the true density or specific gravity of the water to avoid significant cumulative errors, especially when working with low-gravity heavy oils or concentrated brines. Thus, water samples taken for providing input to these programs must have accurate densities determined experimentally.