due to/owing to
This is another of those ‘strictly speaking’ problems. Chambers Dictionary says that due to means ‘caused by’ with a second definition of ‘owing to, because of’, which, it adds, is ‘a use still deprecated by some but now almost standard’. So, for the benefit of the pedants among us:
Due to means ‘caused by’.
Owing to means ‘because of’.
To determine which to use, decide whether you would replace due to or owing to by caused by or because of.