If you have white smoke coming from your cars exhaust then it's a sure sign of a warped head or bad head gasket that is causing coolant loss.
When you have a bad head gasket or warped engine head it allows the coolant to seep into one or more of your engines cylinders which then gets into the combustion chamber of your engine causing it to put out white smoke out of your exhaust.
If you have white smoke coming out of your exhaust you need to get a mechanic to look at it before you do more severe damage to the engine.