Can we analyze premise plumbing systems in WaterGEMS / WaterCAD ?

Product(s): Bentley WaterGEMS, WaterCAD, OpenBuildings Designer
Version(s): Connect Edition
Area: Layout and Input


Can WaterGEMS / WaterCAD analyze premise plumbing systems and get the hydraulic outputs like pressure, water quality etc? If yes, what is the workflow?


To start with Premise plumbing, as we know it includes that portion of the potable water distribution system associated with schools, hospitals, public and private housing, and other buildings. It is connected to the main distribution system via the service line.

Generally, OpenBuildings Designer – OBD is used to handle all of building design, but it also needs to be considered that pressure and water quality could deteriorate in the customer’s plumbing system, so it is necessary to carry out the hydraulic design as well. Which can be done in WaterGEMS / WaterCAD.

Water distribution modeling tools WaterGEMS / WaterCAD, can do the calculations of pressure and determine water quality, provided you know the right coefficients to describe the underlying processes to get the correct results.

The workaround here is to first use OpenBuildings Designer – OBD or e.g. Revit if you have been using it, for designing the buildings, determining fixture units, to lay out pipes etc. And later those 3D models can be exported to WaterGEMS / WaterCAD to perform hydraulic calculations like pressure, water quality, pipe flows etc. 

Note : WaterCAD / WaterGEMS has the capability to export the hydraulic model as i-model.

Hydraulic Calculations -

WaterCAD / WaterGEMS support two dimensional drawings, so the problem lies in handling the multistory plumbing system, but there is a solution for that.

In that case you would need to break down each floor separately and accurately in plan view and connect each floor to the building’s riser pipe (e.g. in red below). An example for a three-story building with each floor laid out side by side shows how this can be done in WaterGEMS / WaterCAD.


With such a model it is possible to dynamically calculate properties such as pressures and flows. The below graph shows how pressures can fluctuate over the course of three days on different floors of a building. The red line shows reasonable pressure at the bottom floor but only marginally acceptable pressure (green line) at the top floor, which is expected as the height rises pressure will be low.


About Water quality -

Water quality analysis includes analyses like  age, constituent, trace etc. Constituent analysis of disinfectants like chlorine, fluoride etc. might of interest here, but age could be the major factor. 

As we know some buildings have rooftop or other in-building tanks which serve to provide reliability and pressure equalization during the day times and store water in case of emergencies. These tanks, however, increase water age and the accompanying disinfectant decay. This can be modeled showing different parameters associated with the tank as per the data available with you.

Below screenshot shows the water age wrt time and flow fluctuations over the time.

Since the use of water is less during night the tank fills and water age increases, whereas in the daytime water age would drop and disinfectant residual stays high. So, these kind of water analysis like water age, water quality standards like constituent analysis also can be performed in premise building models as well, you just need to have sufficient data. These results will help you operate the system efficiently.  

To summarize this we can say, modeling can help building operators better understand the behavior of their systems and improve system performance.

See Also

Connecting pipes to plumbing fixtures 

Getting data and setting up for a Constituent Analysis in WaterGEMS and WaterCAD