Forward osmosis methods and apparatus using a controllable osmotic agent to establish or enhance an osmotic forward bias are disclosed. In a conventional osmosis environment, a controllable osmotic agent is selectively added to an effluent to establish or enhance an osmotic imbalance that favors transfer of an influent solvent to the effluent. After desirable transfer of the influent solvent to the effluent, the controllable osmotic agent is isolated, removed or neutralized so that the transferred solvent and/or concentrated influent can be recovered. The controllable osmotic agent comprises a composition that is reactive to an external influence that does not appreciably affect the effluent solvent, for example, magnetic forces, electrical charges and filtration. Batch and continuous process methods and apparatus are also disclosed.