The invention is directed to apparatus for treating water by exposing the water to a pulsed plasma discharge. The pulsed plasma discharge is generated using a suitable electrode configuration to generate the plasma discharge in the fluid. Apparatus useful in the method may include a vessel, at least two electrodes for generating a plasma discharge in water, and a flow inlet and a flow outlet to allow water to be passed through the vessel. Also described is an in-line water treatment, where a pulsed plasma discharge is used in a pipe carrying moving water. Plasma based fluid treatment system may have many advantages in comparison to other treatment methods, such as very minimal maintenance, low operating power, and minimal pressure loss through the device.