Water in oil can be measured in 3 ways: on-site by sampling, in the laboratory and on-line in real time.
1. On-site measurement
1.1 Crackle Test is the most expedient and economical way to determine water content in oil. Two drops of oil are placed on a hot surface (130℃) and any bubbling or crackling is observed. The size of bubbles may give an indication of the amount of water in the oil. However, due to its course and unitless results, a crackle test is suitable only as a screening test.

1.2 Calcium Hydride Test is one of the most widely used methods on-site; this method uses a pressurised call containing the oil sample and a chemical reagent (calcium hydride). Water in the oil reacts with the calcium hydride and forms hydrogen gas. The cell is shaken vigorously to accelerate the reaction. A change of pressure due to the hydrogen build up is detected by a pressure sensor and this is converted to a water content figure, either in percent (%) or part per million (ppm). The advantages of this method are a very fast turnaround (less than 4 minutes per test) and a low cost per sample.

2. Laboratory measurement
2.1 Karl Fischer Method: one of the more accurate water tests, able to measure as low as 10 ppm of water in oil, but usually only available at a full service laboratory. A disadvantage of the Karl Fischer water test is that it is expensive and ofter time consuming when water concentrations are high.

2.2 Fourier Transform Infra-Red is used as a rapid test for multiple parameters on an oil sample. Infra Red light is passed through a sample of oil and the absorption at different wavelengths in the optical spectra is measured and from this, the concentration of water can be determined. This technique also allows Nitration, Oxidation, Soot Concentration, Phosphate Anti-Wear and Anti-Oxidant depletion amongst other parameters.

3. On-line measurement (Real Time measurement)
3.1 Moisture Sensor: As the critically of water ingress increases, continuous monitoring of water in oil may be needed. On-line Moisture Sensors can be installed on equipment where continuous, 24/7 monitoring is required.

3.2 On-line Infra-Red measurement