Product design specification considerations The product design specification development for the Water sub-system takes consideration of various factors (Daryll, 2008: 98). The factors are well illustrated in the diagram attached below; The diagram presumes that there is already a product conceptual design and hence focuses on deciding on of design shape, material selection, and selection of a process to make the design. An output of any design should clearly detail the way in which the product is made and its standard manufacturing/processing procedures (Singh, 2001: 67). The specification takes into account the manufacturer’s capability, materials relative performance, the behavior of the target market and functionality of the overall system (DETR, 2000). Plumbing system decision matrix           Criteria                                                                                Idea      Complexity & Implementation  Temperature Accuracy * 2  Thermal Capacitance * 1.5  Total Weight    1                            2                         1.5                        4.5   Design 1  4.00                         6.50                      4.50                       15.00 Design 2  3.00                         9.50                      6.38                       18.88 Design 3  2.00                         4.00                      4.50                       10.50 Design 4  2.25                         4.50                      3.75                       10.50  The criteria is described to encompass flexible PDS criteria but were more specific to plumbing systems. The criteria of complexity and implementation are related to the flexible PDS criteria of the system being powering set-up, repeatability of measurement, reduced temperature setup time, and progressive heating/cooling supply temperature (Belfast Engineering Institute, 2009). The criteria of temperature accuracy and thermal capacitance refer to high measurement repeatability and constant heating/cooling supply temperature. The thermal capacitance is a phrase used to describe the amount of energy that will be absorbed into (or from) plumbing parts between the temperature source and the puck. Plumbing systems for a building water system is made up of pipes, fittings, and water tanks as appropriate (Frankel, 2005). The most common pipes used are either metallic or plastic pipes. Fittings are used in coupling of pipe lengths, corner turnings, branching of pipes, pipe size reduction or increment and in connecting the pipes to fixtures like tanks among others. Pipes are often customized to fit the purpose for which they are intended. They differ in diameter, material and make-up depending on the purpose for which they are intended. Indoor pipes are mostly made of copper and galvanized iron with diameters ranging from ½ inch, ¾ inch to 1 inch. Some water supply pipes are made from plastic materials. Ice makers, dispensers for hot water, water filters among others receive their water supply via plastic /flexible copper tubing of reduced diameter (Cummings, 2008). Fittings used are often made of brass or plastic. The double line orthographic drawing below describes the sample piping systems that is to be used in a house building. As seen the piping system is made up of pipes, flanges, connectors and valves. Figure 1: sample piping. The single-line orthographic drawing below describes the water system for the building. Pipes with l