These electrostatic effect give rise to a shrinkage of the water. In this way the field tends to disrupt hydrogen bonded structures in liquid water, and to compress the water molecules surrounding an ion. Temperature changes effect seawater density: as water cools its density increases. The interaction of the electrostatic field of an ion with water tends to align the dipolar water molecules in the direction of the field. See this excerpt from a study on the volumetric effects due to ion-solvent interaction in aqueous electrolyte solutions: In this more ordered arrangement, the ions effectively fill the voids between the water molecules, and the volume of the water only increases slightly. The positive Hydrogen ends of the water molecules are attracted to the negatively charged Cl ions, and the positive oxygen ends are attracted to the positively charged Na ions. This means that at a depth of 1 km, the water pressure is approximately 100 atmospheres or 101.3. The rounded value of 1 g/ml is what you'll most often see. Actually, the exact density of water is not really 1 g/ml, but rather a bit less (very, very little less), at 0.9998395 g/ml at 4.0 Celsius (39.2 Fahrenheit). In the context of ocean water density, water pressure increases with depth at a rate of 1 atmosphere for every 10.06 metres of descent. A common unit of measurement for water's density is gram per milliliter (1 g/ml) or 1 gram per cubic centimeter (1 g/cm 3 ). Because of the geometry of water molecules, they are essentially dipoles with “positive and a negative ends”. The reality is that water is compressible, albeit a very small amount, and only noticeably so at high pressures. Interestingly, the dissolved salt does not increase the volume of the water by the volume of the added salt, and this is due to the charge of the Na and Cl ions and the H 2O molecules. When salt (sodium chloride or NaCl) dissolves in water, there is a significant increase in mass of the solution due to the relatively higher molecular mass of the dissolved ions Na (22 g/mol) and Cl (35.5g/mol) when compared to water or H 2O (20 g/mol).

Sea water density