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This paper considers the introduction of a contaminant into a water supply system using a backflow attack. The recent development of techniques for water network sectorization, aimed at improving the management of water systems, is also an efficient way to protect networks from intentional contamination and to reduce the risk of the dangerous effects of network contamination. Users can be significantly protected by isolated district meter areas (i-DMAs) in the water network and the closing of the gate valves by a remote control system to implement such i-DMAs in cases of malicious attacks. This study investigates the effects of different approaches for water network partitioning and sectorization to protect networks using a technique for designing i-DMAs that is compatible with hydraulic performance and that is based on graph theory and heuristic optimization.For this analysis, the introduction of cyanide through a backflow attack was assumed. The methodology was tested on a large water network in Mexico and displayed good protection from a malicious attack.

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Water Network Sectorization (WNS) consists of dividing a water system into sectors with an independent water supply. When each district is supplied by its only water source the districts can be defined as i-DMAs (isolated District Meter Areas) because they are completely cut off from the rest of the water network. This isolation of the i-DMAs may decrease hydraulic performance of the water system reducing its topologic (network loops) and hydraulic (diameter sections) redundancy. Traditionally the design of WNS is carried out by empirical or simulation assisted trial-and-error approaches that are difficult to apply to large water distribution systems. In this paper an original methodology for automatic sectorization of water networks is proposed. The methodology is based on Shortest Path techniques that allow defining a tree graph of the network with dissipated power used as weight of the pipes (or links). Once the districts are found, a swapping phase follows which is achieved by using a genetic algorithm (GA) that allows refining the choice of nodes that belong to each district. The objective function of the GA is based on network mean pressure. The methodology was tested, using different performance indices, on two real water supply systems.