Systems and methods for removing a contaminant from a liquid are generally described. The liquid (e.g., water) containing the contaminant may be flowed across a semipermeable membrane (e.g., via forward osmosis) that is not permeable to the contaminant in order to remove the contaminant from the liquid. A concentration gradient across the semipermeable membrane may be provided and maintained by electrolysis of the liquid and can drive forward osmosis of the liquid through the semipermeable membrane.