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The municipal and departmental councils of the inner suburbs of Paris, in charge of sanitation for the conurbation, must build and upgrade sewerage to respond to current and future urban use. Geographical research on time in spatial systems is useful for understanding local and regional governments' development choices. The inclusion of time in the action/reaction loop and the concept of «localised/localising events» are fundamental for explaining the duration of the sewer system. The malfunctions in existing facilities and the choices for new facilities are examined through public and private uses and their pace and history.