Notified by local residents, the city’s Public Works Department detected the presence of non-potable water in the public supply network. The DDASS Human Health and Welfare Office was duly informed. Investigations carried out by Department staff blamed a neighbouring industry that had performed works on its own water supply network a few days prior. This factory was being fed by 2 parallel inlet pipes, while its industrial water system was hooked up to a river pumping station. These pipelines, connected to the municipal network, were isolated by shutoff valves and check valves. During these works, workmen had indiscriminately handled the cut-off valves, thus opening the industrial network to other flows. The check valve malfunction placed the industrial water circuit (at 3.5 bar) in direct contact with the public supply network (2.5 bar). The valve, which was opened by mistake and then closed, later revealed a breached seal. According to the facility’s Environmental Manager, the mingling of potable and industrial water was only detected 6 days hence; during this time, the potable network was polluted by water pumped from the river: 370 dwelling units (accounting for 1,100 residents) were adversely affected. The DDASS Office recorded some 60 cases of sickness (6 of them required hospitalisation) and another 400 people felt ill effects. The facility was repaired, and a backflow prevention device installed. Public Works staff drained and disinfected the contaminated part of the public network. Inspection Authorities, informed belatedly about this pollution incident, logged the facts and proposed that the Prefect order additional measures be taken. Subsequent to this accident, the network operator was requested to install backflow prevention devices on all pipelines tied into the city’s drinking water supply network.