System for supply of liquid

A system for supplying liquid comprising a tapping point (15) for drawing off liquid from the system, a liquid pipe (4, 5, 12, 13, 16, 18) that connects the tapping point with a flow regulator (2, 41), which in an active mode passes liquid from a liquid source (1, 40) through the pipe to the tapping point and in an inactive mode prevents the flow of liquid through the liquid pipe, a liquid purifier (6), which is connected to the liquid pipe between the tapping point and the flow regulator and which comprises an electrical UV light source (10) and means for automatically lighting up the UV light source (10) when the flow regulator (2, 40) is activated for passing liquid through the liquid pipe and the tapping point, characterized in that the flow regulator (2, 41) is controlled electrically and is connected to a voltage source (21) via an electrical supply lead (241, 24b, 42a, 42b) and in that means for automatically lighting up the UV light source (10) is arranged to detect a supply current that passes through the supply lead when the flow regulator is activated and to light up the UV light source when the supply current passes through the supply lead.