Using a Genetic Algorithm with a Mathematical Programming Solver to Optimize a Real Water Distribution System

2. Water Distribution Problem (Case Study) 

The water distribution problem can be represented by graph theory. A graph is denoted as 𝐺 =

(𝑉, 𝐴), where  𝑉  is a set of vertices or nodes and  𝐴  is a set of edges or arcs. There are different types 

of graphs. Non-directed graphs have two directions, and directed graphs have only one direction 

[36]. Figure 1 shows the graph of the FRM network, which is a directed graph because the water flows 

in one direction. In this graph, the nodes represent supply sources (reservoirs, tanks) or points of 

consumption (homes, shops, industries, etc.). They are represented by different symbols depending 

on whether nodes are sources or points of consumption (Table 1). The edges represent the connecting 

elements such as pipes, valves, and pumps. Each edge has an associated cost which can be the cost 

of the pipe diameter, the flow velocity in the pipes, the length of a pipe, the cost of the valve, the cost 

of the pump or another parameter. This representation is important because it is exactly the input 

parameter that EPANET solver needs to find the hydraulic characteristics of the network, such as 

pressures, and velocities, among others. 

Table 1 shows the symbolic representation of the elements in a network. Some symbols are 

presented in the original FRM network (Figure 1), such as tanks, reservoirs, consumption points, and 

pipes. Pumps and valves are not represented in the graph because they do not exist in the current 

FRM network. 

Table 2 summarizes the main elements of the FRM network. There are 364 pipes with a diameter 

of 22.7 to 101.6 mm. The minimum pressure requirement is 10 mca (meters for water column) and 

the maximum pressure requirement is 60 mca. The standard demand (pro-capita amount) is the 

amount of water needed for each node of the FRM network.