An electrochemical reactor for electrochemically treating water, including a shell structure defining an inner space. The shell structure further includes an inlet portion having an inlet for conducting a water flow to the inner space, and a reactor chamber in flow connection with the inlet portion, and preferably with an outlet portion. The inlet is arranged such that the water flow to the inner space is directed away from the reactor chamber so as to cause the water flow to mix by forcing the water flow to change direction before entering the reactor chamber. A water treatment apparatus having such a reactor, and the use of such a reactor are also disclosed.