Properties of Water (0–100 °C)
Density, dynamic and kinematic viscosity, vapour (saturation) pressure, and specific heat of liquid water at atmospheric pressure, in 5 °C steps. Values are computed from IAPWS-IF97 — the international standard water formulation — using the same property functions SimuPipe's solver evaluates during a simulation.
Water properties vs temperature
| T (°C) | Density ρ (kg/m³) | Dyn. viscosity μ (mPa·s) | Kin. viscosity ν (mm²/s) | Vapour pressure Pᵥ (kPa abs) | Specific heat cₚ (kJ/kg·K) |
|---|---|---|---|---|---|
| 0 | 999.84 | 1.753 | 1.753 | 0.6112 | 4.220 |
| 5 | 999.97 | 1.501 | 1.501 | 0.8726 | 4.205 |
| 10 | 999.70 | 1.300 | 1.300 | 1.228 | 4.196 |
| 15 | 999.10 | 1.136 | 1.137 | 1.706 | 4.189 |
| 20 | 998.21 | 1.002 | 1.004 | 2.339 | 4.185 |
| 25 | 997.05 | 0.890 | 0.893 | 3.17 | 4.182 |
| 30 | 995.65 | 0.797 | 0.801 | 4.247 | 4.180 |
| 35 | 994.04 | 0.718 | 0.723 | 5.629 | 4.179 |
| 40 | 992.22 | 0.651 | 0.657 | 7.384 | 4.179 |
| 45 | 990.22 | 0.594 | 0.600 | 9.594 | 4.179 |
| 50 | 988.05 | 0.544 | 0.551 | 12.35 | 4.180 |
| 55 | 985.71 | 0.501 | 0.508 | 15.76 | 4.181 |
| 60 | 983.21 | 0.463 | 0.471 | 19.95 | 4.183 |
| 65 | 980.57 | 0.430 | 0.438 | 25.04 | 4.185 |
| 70 | 977.78 | 0.400 | 0.410 | 31.2 | 4.188 |
| 75 | 974.86 | 0.374 | 0.384 | 38.6 | 4.192 |
| 80 | 971.80 | 0.351 | 0.361 | 47.41 | 4.196 |
| 85 | 968.62 | 0.330 | 0.341 | 57.87 | 4.200 |
| 90 | 965.32 | 0.311 | 0.323 | 70.18 | 4.205 |
| 95 | 961.90 | 0.294 | 0.306 | 84.61 | 4.211 |
| 100 | 958.45 | 0.279 | 0.291 | 101.4 | 4.217 |
Liquid water at 1 atm (the 100 °C row is saturated liquid). 1 mPa·s = 1 cP = 0.001 Pa·s; 1 mm²/s = 1 cSt. Vapour pressure is absolute. cₚ is the isobaric specific heat of the liquid.
Definitions & Key Relations
Kinematic viscosity is dynamic viscosity divided by density:
- — kinematic viscosity (m²/s; 1 mm²/s = 10⁻⁶ m²/s)
- — dynamic viscosity (Pa·s; 1 mPa·s = 10⁻³ Pa·s)
- — density (kg/m³)
Both forms appear in the Reynolds number, which sets whether pipe flow is laminar or turbulent:
- — mean velocity (m/s)
- — internal pipe diameter (m)
Because μ halves between 20 °C and 50 °C while ρ barely moves, the Reynolds number of the same flow roughly doubles — hot-water systems are more turbulent, with slightly lower friction factors, than a cold-water calculation predicts. Vapour pressure enters the NPSH available at a pump suction and the cavitation check for control valves: see the NPSHa vs NPSHr guide.
Data source and basis
- Density, vapour pressure, and specific heat are evaluated from IAPWS-IF97 (the international standard industrial formulation for water and steam): density from the Region 1 liquid equation at 1 atm, vapour pressure from the Region 4 saturation equation, cₚ for the saturated liquid.
- Dynamic viscosity uses a Vogel-form fit that stays within a few percent of the IAPWS viscosity formulation over the liquid range (0.03% off the reference 1.002 mPa·s at 20 °C, ~1% at 100 °C).
- These are the same property functions SimuPipe evaluates when you set a fluid temperature in a simulation — the table is a view of the application's data, not a separate transcription. Spot anchors: ρ = 998.21 kg/m³ and Pᵥ = 2.339 kPa at 20 °C match published IAPWS-IF97 tables to 4 significant figures.
- For saturated and superheated steam properties (enthalpy, entropy, latent heat), see the steam tables calculator.
Frequently Asked Questions
What is the density of water at 20 °C?
998.21 kg/m³ (0.99821 g/cm³) at 20 °C and atmospheric pressure, per IAPWS-IF97. Water is densest at about 4 °C (999.97 kg/m³) and gets lighter as it warms — at 100 °C the liquid is about 958 kg/m³, roughly 4% lighter than at 20 °C. For most pipe-flow calculations at ambient temperature, 998 kg/m³ (or simply 1000 kg/m³ for rough work) is the value to use.
How much does water viscosity change with temperature?
A lot — far more than density. Dynamic viscosity falls from 1.75 mPa·s at 0 °C to 1.00 at 20 °C, 0.54 at 50 °C, and 0.28 at 100 °C: heating water from 20 °C to 50 °C roughly halves its viscosity. Since pressure drop in laminar flow is proportional to viscosity, and the friction factor in turbulent flow also depends on it through the Reynolds number, using a 20 °C viscosity for a 60 °C system materially overstates friction loss.
What is the difference between dynamic and kinematic viscosity?
Dynamic (absolute) viscosity μ measures resistance to shear, in mPa·s (numerically equal to centipoise, cP). Kinematic viscosity ν is dynamic viscosity divided by density, ν = μ/ρ, in mm²/s (numerically equal to centistokes, cSt). For water the two happen to be numerically close because water's density is close to 1000 kg/m³. The Reynolds number can be computed with either: Re = ρVD/μ = VD/ν.
What is vapour pressure and why does it matter for pumps?
Vapour (saturation) pressure is the absolute pressure at which water boils at a given temperature — 2.34 kPa at 20 °C, rising to 101.42 kPa at 100 °C. If the local pressure anywhere in a system falls below it, the water flashes to vapour: this is cavitation. It governs NPSH available at pump suctions and the choked-flow limit of control valves. The hotter the water, the higher its vapour pressure and the easier it cavitates — which is why hot condensate service is hard on pumps.
Does pressure affect these liquid water properties?
Only weakly. Liquid water is nearly incompressible: raising the pressure from 1 bar to 10 bar increases density by only about 0.04%, and viscosity is similarly insensitive at moderate pressures. Temperature is the variable that matters. The values in this table are at atmospheric pressure; they remain accurate for typical pumped-system pressures. (Vapour pressure, by definition, depends on temperature only.)
What about water above 100 °C?
Above 100 °C, liquid water exists only under pressure (a boiler feed line at 150 °C needs at least 4.76 bar absolute to stay liquid). The correlations behind this table remain valid for pressurised hot water up to about 350 °C — SimuPipe evaluates them at your set fluid temperature automatically, and its saturation check warns when a node's pressure falls below the vapour pressure so accidental flashing is flagged rather than silently mis-solved.
Simulate with temperature-correct water properties
Set the fluid temperature once — SimuPipe evaluates density, viscosity, and the vapour-pressure cavitation check at that temperature across your whole network.