## 4 Proposed Workflow for DDWSS Design
### Inputs for Automation  
For conceptual design, the preliminary information on the structure is delivered by an architectural design that provides the basic conditions for DDWSS operation, such as the type of building, the location, the number of occupants or users, the estimated consumption and the existing public distribution and collection networks [26]. It is then necessary to define the type, location and quantity of artefacts used in the building in order to connect them and create a system through a manual routing process. The purpose of the manual routing process is to facilitate the modeller's freedom and establish criteria for the design of the network. Within the routing process, the materials and preliminary diameters of the pipes must be assigned, as well as any mechanical systems that may be required [40].  
As a preliminary step for the generation of BIM project models, the different elements used for the calculations must be configured in Autodesk(r) Revit(r), especially those belonging to MEP systems. These elements are included by default with predefined parametric values. Autodesk(r) Revit(r) contains a database of default families and family types, the configuration of which is predefined according to International Plumbing Code (IPC) specifications. It is necessary to modify and integrate objects' families according to the regulations relating to their characteristics, dimensions and mechanical parameters applicable in the country where the automation process will be applied. This also applies to pipe families, for which--although they have a predefined database--it is necessary to add new family types. In the case of materials, it is necessary to add those that are available in the market and those that are increasingly used to establish the commercial diameters for the modelling.  
Regarding the system's artefacts, for each sanitary fixture, the corresponding acronym, installed flow rates, height and inlet and outlet diameters must be defined. Each pipe section drawn will be subject to both geometrical and mechanical constraints, so it is important to consider the performance of the connections of the elements in the model when building the piping system. It is thus necessary to undertake detailed modelling of each component of each system. All the fittings and connectors must be described and positioned consistently in order to avoid any deviations or differences in the data readings provided by the model. Moreover, the modeller must correctly select the type of system to which each traced pipe belongs; i.e., the cold-water, hot-water or drainage systems.  
In sewerage systems, it is important to indicate the intended use of the sanitary fixtures according to the type of building and the number of people to be served in order to correctly define the wastewater flow that returns to the public system. Water flow sewage systems are gravity-fed; therefore, certain considerations must be taken into account when laying out the pipes so as not to generate points at which solid waste can be deposited and obstruct the continuous discharge of the flow. According to the regulations, a minimal pipe slope must be provided to allow for self-cleaning, the creation of geometries with closed singularities should be avoided and manholes should be placed correctly.