What causes a Range Rover to blow white smoke?

Generally speaking, black smoke is fuel; blue/grey smoke is oil; and white smoke

is water. Heavy white smoke is trans fluid. On a Range Rover it can only be water. The bad news is you have a blown head gasket or worse, depending on the year. if your Rover is 4.0/4.6 you could also have a slipped sleave in your engine block. This is common on higher millage engines, but I have seen it as early as 55k miles. Perform a block test to verify. Also remove the center 2 spark plugs on each side and check for pink/orange discoloration that looks like coolant.