Probably a silly question but have you changed the diesel filter? A blocked filter will cause all kinds of trouble including poor starting, white smoke, black smoke etc. I would also be tempted to give it a good long run, not just idling on the drive. White smoke does indicate water but can also be caused by condensation sitting in the exhaust, an engine produces an awful lot of water when cold and if not driven far enough to dry it out it will smoke when you start the engine again.
Bloody Commer`s!