An example water purification system includes a forward osmosis module, a reverse osmosis module, a pump powered by an electric motor, and a pressure sensor. The forward osmosis module may receive a feed stream and a draw stream, and may produce an intermediate product stream. The intermediate product stream may be pressurized by a pump and provided to the reverse osmosis module. The reverse osmosis module may generate a product stream and return the draw stream to the forward osmosis module. The pressure sensor may monitor the pressure of the intermediate product stream, and the pressure may be used to determine the speed of the electric motor.