Water is considered an incompressible fluid because its compressibility is extremely low compared to other substances. This means that even under high pressures, water does not significantly change in volume. Therefore, for most practical purposes, the compressibility of water can be considered negligible.
Water's compressibility is measured by its bulk modulus, which is a measure of how much pressure is needed to cause a given percentage decrease in volume. For water, this value is approximately 2.2 x 10-9 Pa-1, which is significantly lower than most other liquids and gases.
The compressibility of water is affected by temperature, pressure, and salinity. As temperature and salinity increase, water becomes more compressible. However, even at extreme temperatures and pressures found in the deep ocean, water's compressibility is still considered negligible.
The negligible compressibility of water is important in engineering because it allows for accurate calculations and predictions when designing structures or systems that involve water. For example, when designing a dam or a submarine, engineers can assume that the volume of water will not significantly change, making it easier to determine the necessary dimensions and materials.
While water is considered an incompressible fluid, it can still be compressed to some extent. However, to achieve a significant change in volume, extremely high pressures are needed. For example, to compress water by just 1%, a pressure of over 2200 atmospheres (32,000 psi) is required.