Forward osmosis (FO) is a low-energy membrane technology of great interest for water reuse and desalination. A critical step for making FO practical is selection of proper draw solutes. We synthesized superhydrophilic, citrate-coated magnetic nanoparticles (cit-MNPs) through a co-precipitation method, and then systemically investigated their osmotic potential as draw solutes for FO. The adaptability of cit-MNPs as draw solutes was ensured by their special characteristics (highly negative surface charge and high surface charge density). The initial FO performance was a pure water flux of 17.3 LMH with 20 mg/L MNP in FO mode, however a rapid decline in the water flux occurred due to an interaction between the cellulose triacetate (CTA) membrane and cit-MNPs. A magnetic field control (MFC) FO module was introduced to optimize the use of the cit-MNPs. Magnet field drives the magnetic particle away from the CTA membrane. In MFC FO module, a stable FO initial water flux of 13 LMH resulted with 20 mg/L MNP in FO mode. Our experimental results demonstrated that cit-MNPs can be suitable draw solutes for the FO process and the proposed MFC FO module is believed to be the first device for increasing water flux using magnetic nanoparticles as draw solutes. (C) 2014 Elsevier B.V. All rights reserved.