The coolant level's should not drop unless there is a leak in the system.
Check for any visual leaks if non then you got bigger problems.
Could be the Head gasket. could also be a cracked turbo on the water channel as from what i understand coolant does run through for cooling purposes and now coolant is being burnt in the turbo hence the white smoke speak under correction.
Also what car is this?
2011 C63 AMG
2008 RS Golf 5 Gti DSG
2006 Velociti 1.6i
2014 Polo 6R Comfortline
2005 325i Individual
1990 Gli Twincam 4AGZE Supercharged
2000 Audi A3 1.8t
1996 Toyota Corolla 160i GLE