Since 1970, Lyonnaise des Eaux has developed a policy of automation at its water treatment plants. Originally based on solid logic modules, the technology used was upgraded and improved in the late seventies by the progressive and extensive use of programmable logical controllers (PLC). Since 2nd of May 1984, the potable water production of the western suburb of Paris (1 million inhabitants) has been fully automated (with around 100 PLCs), and unmanned after hours. Over the years, PLC has been progressively used for supervisory control and data acquisition (SCADA), for chemical treatment closed loop regulation and for more sophisticated hydraulic balance regulation of waterworks. In most process control and SCADA systems, PLCs are mainly used for real time process control and data collection when remote terminal units (RTU) are used for stamp dated data communication protocol and monitoring purposes on distribution networks. SCADA systems are now built as patchworks of various brands and types of equipment (when necessary). (6 pages)