Operational control essentially aims at checking the water quality level for human consumption throughout the entire supply system and detecting possible abnormalities in time - either occasional or systematic - as to allow for efficient preventive measures.

Operational Control/Watch is carried out systematically in approximately 180 fixed sampling points within Lisbon's Distribution Network, 58 representative points within the Adduction and Transport System, and 51 sampling points located in the water origins (superficial and underground).

The process is controlled in the treatment plants by collecting water samples to be analysed within the treatment processes installed in the Asseiceira and Vale da Pedra water treatment plants as well as Alenquer's intake enclosure for treatment efficiency control. The control of liquid effluents and mud generated in Asseiceira and Vale da Pedra water treatment plants shall also be considered. This process is controlled using 106 sampling points.