White Smoke = Water?

[Crazy Dazz]

So, after sitting all day in the car park, when started, my daughter's car starts billowing white smoke.
However, after being idled for a while, then left to cool, and re-started, no sign of anything unusual.

To me, white smoke means water (coolant) being burnt.
So I'm thinking: Car driven to work, gets nice and hot, under pressure head-gasket starts to leak. When car is parked, continues to leak under pressure and builds up in cylinder. Car is started, burns off coolant and eventually purges all from exhaust. Engine turned off, not too hot, so no further leakage. Starts fine next time round.

The coolant looks fine, as does the oil. The coolant level was still ok.

So, with the engine cold we have topped the coolant to a precise level. Will drive the car to work, park it up, then check the level in the evening when its cold again.

It's also possible that it was simply a bunch of condensation after being driven and then parked on a cold day.

Am I missing anything?
Any other possible culprits for white smoke?

NB: It is a Nissan Tiida, with a typical, disposable, Thailand engine. So it's not improbable that the gasket or head has started to dissolve.