An Insidious Contaminant: Water in Oil

Water. Necessary to support life, covers the majority (~71%) of the Earth’s surface and exists in almost every facet of everyday life. However, there are certain substances to which the absence of the aforementioned liquid is critical, including a variety of oils.

The International Organization for Standardization (ISO) Cleanliness Code attributes a 10-30% increase in lifespan of related components and instrumentation through the reduction of particle contamination. Moisture contamination is a close second when it comes to component destruction in related oil systems (engines and transformers, as examples) and therefore it needs to be minimised where possible and detected through analysis.

The State of Water in Oil

Water can be considered the ‘Cerberus of Contaminants’ when it comes to oil – as it can be categorized in three distinct forms: Dissolved, Emulsified and Free Moisture. Each can potentially cause issues, but it is generally agreed that Emulsified and Free Moisture are the most harmful phases, dependant on the system the oil is present within.

Dissolved water can be compared with evaporated water in the air on a humid day, you know it’s there but it’s too small to see. The oil is characterised by individual water molecules dispersed within the oil, often anywhere between 5-600 ppm (dependant on the oil type and age in question).

Once the dissolved moisture reaches a saturation point, any additional water molecules will begin to precipitate as emulsified micro-droplets. These can behave unexpectedly and cause the oil to ‘visibly haze’ (think how water moisture can cause fog). If water continues to be added to an emulsified oil, then a complete separation can occur, leading to a free layer of water forming (and generally sinking) within the oil.

The Damage of Water Contamination

This all begs the question – what damage can water contamination within an oil cause?

Dissolved moisture can degrade metal and deplete additives within the oil. Any polar metal will attract the water molecules and potentially through heat and pressure cause the release of hydrogen ions. The hydrogen ions will chemically degrade metal and the release of metal particulates can lead to corrosion and further issues.

Emulsified moisture can directly increase the compressibility of the oil, which can damage parts within the system containing the oil. Like dissolved moisture, the same corrosion and rusting can occur, and the particulates can also combine with the emulsified water to form a sludge! This sludge can cause a vicious cycle, causing greater damage to metal at a faster and faster rate and potentially clog oil filters. Furthermore, acidification of the oil is exacerbated by emulsified moisture, leading to a greater rate of metal corrosion.

Free moisture is almost identical in terms of how it is damaging with emulsified moisture – but due to the density it will sink and cover polar metals in a film of water molecules. This will cause a substantial increase in the rate of rust, corrosion, and fracture of affected metal.

So, it is evident that water can be highly destructive when allowed to contaminate oils. How can we ascertain moisture levels in a sample of oil?

Measurement of Water: Crackle Test

The classic (albeit slightly outdated) method for testing water within oil is known as the ‘crackle test’. It is almost exactly as described by the title; a droplet of oil is dropped on a hotplate set at ~160oC and the vaporisation of water can lead to an audible crackle/pop. The higher the number of ‘pops’ heard, indicates a higher water content of the sample.

While this method certainly isn’t quantitative, it is cheap, rapid and simple! Within analytical chemistry, it should only be employed in addition to a more accurate method that can provide quantitative data.

Eliminate the Uncertainties: Moisture Meters and Karl Fischer

We at a1 envirosciences appreciate that time is valuable, and the correct information is vital in formulating a successful predictive maintenance strategy. This is why we offer the CA/KF-31 Moisture Meter.

Through quantitative moisture measurement, there is no grey area when it comes to oil analysis, just a rapid and accurate quantitative reading. It’s also highly mobile, meaning you can take ‘the lab to the sample’ and test on-site.

FTIR (Fourier Transform Infrared Spectroscopy) can also be employed when analysing the water content of oils and relies on a mathematical algorithm to predict the water content in oil. However, it has a lower resolution when compared to Karl Fischer, and other contaminants (metal particulates for example) can reflect and absorb the IF wavelength employed in FTIR, leading to false positives.


Ultimately there are many reasons to test for moisture within oils, especially mineral and lubricant oils employed in machinery and transformers! Although the crackle test is cheap and easy to perform, it is imperative to employ a more sophisticated analytical technique to ascertain water contamination and minimise the hazard of water contamination.

If you are interested in finding out more about Karl Fischer or the CA/KF-31 Moisture Meter for your oil analysis, give us a call on 0845 873 8181 or get in touch with us by email!