Dear Prochem,
In desalting process , BS&W – Bottom sediment & water is being monitored in inlet and outlet of the desalter – Usually,BS&W gives total % of water present in crude oil – for example, if you are getting 0.5 wt % of BS&W in outlet of desalter,then it contains little amount of soluble water and rest is free water..usually..0.5 wt % of BS&W gives you 0.1 – 0.15 wt % of soluble water & rest is free water.There should be some laboratory testing method which can differentiate amount of soluble water present in BS&W in crude oil.
Regards,