This is normal and nothing to worry about. Some areas of the country have climate that is quite conducive to an engine producing water vapor (white 'smoke') upon cold engine start and for a bit after.
One of the main causes of white exhaust smoke and coolant loss is a cracked or warped cylinder head, a cracked engine block, or head gasket failure caused by overheating. Even small amounts of coolant entering the combustion chamber will produce white exhaust smoke. An internal coolant leak can also contaminate the engine oil giving it a frothy, milky appearance. Indicators of an internal coolant leak include billowing white exhaust smoke accompanied by a sweet odor or a low coolant reservoir level. If excessive white exhaust smoke is present well after the engine warms up, it is necessary to have the car inspected by the dealer for possible internal coolant leaks. As the engine warms up and the condensation dissipates, the white exhaust smoke (steam) is no longer seen.
This is generally steam caused by condensation. It is common to see 'white exhaust smoke' when first starting a car, especially on cooler days. As A Guy has stated, if you only see white water vapor on start-up (i.e., it is not constant), you should be okay.
