Dear Duarte
Acording to ASTM D-4378-03, you shouldn't run water content analysis of the oil.
However, as you know water in the oil up of 100 ppm is in the emulsified form. When you have this high value, you could have problems with the lubrication regime, the oil degradation, and equipment rust.
I think that water content analysis isn't a expensive test, and the result gives you more data for your predictive program.
In some cases you'll find water in Gas Turbines (5-7% of the cases according our experiencies). This water comes from rain, enviroments (Off Shore Platforms), etc.
I hope these comments help you.
Regards,
Cristián Schmid.