The present invention provides a configuration of a multi stage flash cross tube evaporator wherein flash stages are arranged in a plurality of at least two tiers with a first flash stage to which a heated solution is fed, a plurality of intermediate flash stages and a last flash stage from which the concentrated solution is discharged in each tier, wherein the flash stages in each tier are in a serial flow communication and the flash stages of each tier are in parallel flow communication to the flash stages in the other tier(s). Such configuration allows to minimize the size of the tube bundles, flash stages and evaporator shell and consequently minimizing evaporator weight and cost.