Overview
ISO/TR 3666:1998 - Viscosity of water provides internationally recommended reference values for the viscosity of water at several temperatures. The Technical Report defines the dynamic and kinematic viscosity at 20 °C and gives a temperature-dependent viscosity ratio and supporting metrological data used as the basis for calibrating relative viscometers worldwide. Values are referenced to the international temperature scale ITS‑90.
Key topics
- Reference values (20 °C, 1 atm):
- Dynamic viscosity η(20 °C) = 1.0016 mPa·s
- Kinematic viscosity ν(20 °C) = 1.0034 mm²/s
- Estimated relative uncertainty: 0.17 % (95 % confidence)
- Temperature dependence: recommended viscosity ratio V = η(T)/η(20 °C) for T = 15, 20, 23, 25, 30 and 40 °C (e.g., V(15 °C) = 1.1360, V(25 °C) = 0.8885, V(40 °C) = 0.6514).
- Auxiliary data in the report: mass density at each reference temperature, temperature coefficients (Uη and Uν) defined by Uη = −(1/η) (dη/dT) and Uν = −(1/ν) (dν/dT), and the pressure coefficient γ given by γ = (1/η)(dη/dp).
- Metrological basis and provenance: values derived from a critical review of published absolute measurements (1949–1994) and adjusted for the ITS‑90 temperature scale (correction from IPTS‑48 of 12 mK at 20 °C).
- Water quality and handling: values apply to freshly bidistilled water. For viscometers sensitive to surface tension (e.g., capillary types), avoid surfactant contamination; use fused silica equipment for distillation and storage when necessary.
Applications
- Calibration of relative viscometers: serves as the primary metrological reference for routine and high-accuracy calibration of rotational, capillary and other relative viscometers.
- Laboratory quality control: provides traceable reference values for viscosity measurements in testing labs and quality assurance programs.
- Research & development: used in fluid property studies where precise water viscosity values are required across common lab temperatures.
- Petroleum and lubricant industries: supports viscometry standards and calibration practices referenced by technical committees and manufacturers.
Who should use it
- National and industrial metrology institutes
- Calibration laboratories and testing facilities
- Viscometer manufacturers and calibration service providers
- Laboratory technicians and R&D teams requiring traceable viscosity references
Related standards
- International Temperature Scale ITS‑90 (temperature reference used in ISO/TR 3666)
- Other ISO standards and technical documents on viscometry, calibration procedures and laboratory best practices
Keywords: ISO/TR 3666:1998, viscosity of water, water viscosity values, dynamic viscosity, kinematic viscosity, viscometer calibration, ITS‑90, reference temperatures, bidistilled water, metrological basis.
