Water Properties

When pumping water, it is important to understand properties such as the water density or specific gravity and vapor pressure. This section provides tables and graphs of water saturation properties as a function of temperature.

Specific gravity, also referred to as relative density, is the ratio of the densities of one fluid at a known temperature and pressure to a reference fluid at a specific temperature and pressure. In most cases, the reference fluid is water at atmospheric pressure. The most common reference temperatures in the standards and literature are 39.2 °F at which water is the most dense, 60 °F, and 68 °F. Generally, scientific research and common fluids use 39.2 °F while engineering and petroleum applications use 60 °F.

The values for specific gravity of water based on these common reference temperatures are listed in the table below.

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Water Properties at Various Temperatures

Water Saturation Properties

Sat. Properties for Water (Liquid)

Sat. Properties for Water (Vapor)

Auxiliary Data

Reference States, Default for Fluid

Enthalpy

H = 19771.296 Btu/lb-mole at 80.3 °F and 0.15 psia

Entropy

S = 39.198 Btu/lb-mole·R at 80.3 °F and 0.15 psia

Additional Water Properties

Equation of State

The uncertainty in density of the equation of state is 0.0001% at 1 atm in the liquid phase, and 0.001% at other liquid states at pressures up to 1450 psi and temperatures to 761.4 R. In the vapor phase, the uncertainty is 0.05% or less. The uncertainties rise at higher temperatures and/or pressures but are generally less than 0.1% in density except at extreme conditions.

The uncertainty in pressure in the critical region is 0.1%.

The uncertainty of the speed of sound is 0.15% in the vapor and 0.1% or less in the liquid and increases near the critical region and at high temperatures and pressures.

The uncertainty in isobaric heat capacity is 0.2% in the vapor and 0.1% in the liquid, with increasing values in the critical region and at high pressures.

The uncertainties of saturation conditions are 0.025% in vapor pressure, 0.0025% in saturated liquid density, and 0.1% in saturated vapor density. The uncertainties in the saturated densities increase substantially as the critical region is approached.

Reference for Data

Eric W. Lemmon, Mark O. McLinden and Daniel G. Friend, "Thermophysical Properties of Fluid Systems" in NIST Chemistry WebBook, NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, Gaithersburg MD, 20899, https://doi.org/10.18434/T4D303, (retrieved February 19, 2019).