The article continues previous text published in "Management Business Innovation" (no. 6, 2010) under the title Stock-And-Flow Thinking In Decision Making. Towards Systemic Procedure of Problem Solving. The methodology presented there is shown in the practical context of water supply management problem in one of the largest cities in Mexico. Basic methodological implications for computer supported problem modeling and simulation are shown, beginning with the Partitioning&Tearing Method, causal diagram of the problem as well as the computer simulation model structure drawn with the VensimTM software.