The specific gravity of water is the density of water. The specific gravity of water is 1000 kg/cubic meter (t=4℃).

Water has the highest density at 3.98℃ (999.97kg/m?, 1000kg/m? is often used in approximate calculations). The density of solid water (ice) (916.8kg/m?) is smaller than the density of liquid water (999.84kg/m?), so ice can float on the water. When water freezes, its volume increases slightly.

In addition, supercritical water is compressible. Small changes in temperature or pressure will cause the density of supercritical water to be greatly reduced. At the critical point, the density of water is only 0.326g/cm? Typical supercritical water oxidation is performed when the density is close to 0.1g/cm?.

Use of relative density

Based on the relative density of certain substances, certain fire-fighting characteristics can be inferred and corresponding fire-fighting measures can be taken. For example, if a fire occurs with flammable and combustible liquids with a relative density <1, water should not be used to put out the fire, because it will float on the water, not only cannot be saved, but will disperse with the water, increasing the loss. Therefore, foam and dry powder should be used to extinguish fires.

Another example is flammable gases and vapors with a relative density <1, which easily diffuse and form explosive mixtures with air, and easily flow along the ground and ditches over long distances. If exposed to an open flame, backfire will occur. When determining the location of the vents in workshops and warehouses, for gases that are lighter than air, the vents should be located above the space; for gases that are heavier than air, the vents should be located at the bottom of the space.

The above content refers to Baidu Encyclopedia—Water