A bicompartment bag adapted to prepare a liquid solution has an assembly of two flexible outer sheets with an access bushing affixed through one of the sheets. The interior of the bag is divided into two chambers by a third flexible sheet having a screen-like stripe with its distal end located at the bottom of the bag. The third sheet has a bore affixed around its edge onto the annular plane of the bushing end projecting into the bag. The first chamber communicates with, through the bushing, a solvent inlet and is partially filled with powdered solute. The inside of the second chamber has a layer separate from the bag. The second chamber layer, constructed of a woven or injected material, extends from a semicircular recess made in correspondence with the bushing to the bottom of the second chamber. The bushing provides the opening for removal of the resulting solution.