At what percentage does water in oil begin to make the oil appear cloudy?

The correct percentage at which water in oil begins to make the oil appear cloudy is indeed 0.1%. This phenomenon occurs due to the immiscibility of water and oil, where even a very small amount of water can disrupt the clear appearance of oil. This clouding effect happens because the water droplets disperse in the oil, creating a colloidal suspension that scatters light.

Understanding this threshold is essential in various applications, particularly in lubrication and hydraulic systems, where water contamination can significantly affect performance and lead to equipment failure. Recognizing that cloudiness can begin at such low levels highlights the importance of monitoring and managing water content in lubricants and fuels to maintain optimal functionality and reliability.