Water separator for continuous separation of water, air and particles, and a method for controlling said separator, said separator comprising an inlet pipe (5) for receipt of a mixture of water, air and particles from sources such as dental surgeons etc. and an oultet pipe (1) being connection to a suction motor (13), comprising an upper chamber (3) being connected with a lower chamber (4) by a valve (7) in the bottom of the upper chamber (3) and a pipe (12) having a three-way valve (10) for establishing a connection between the upper and lower chambers in one position and closing said connection and allowing atmospheric air into the lower chamber (4) in another position, the lower chamber (4) normally being closed by a check valve (8) in the bottom, and the lower chamber (4) comprising at least one level switch (9).
