Duke SmartHome Graywater Reuse System

gray wa·ter [noun: greywater]

the relatively clean waste water from baths, sinks, washing machines, and other kitchen appliances.


{to design a mechanism that diverts water to storage or sewage according to its quality}


In order to prevent graywater waste in homes, my team (Ale Ferrara and Minhaz Islam) and I proposed a Graywater Reuse System. We took advantage of the cycles in water quality that occur in graywater sources. After researching the various parameters that control the characterization of water as 'graywater', we decided to focus on 3 vital parameters: conductivity, pH and turbidity. Before we began working on the design, we brainstormed the various risks associated with the project. We used the countermeasures developed in this session to create a device schematic (below) to outline our plan. An initial sand filter clears large debris, and then a series connection of transmitters and solenoid valves provide pass-fail test for vital parameters such as conductivity, pH, and turbidity, resulting in the cleanest graywater output possible.

Next, it was time to prototype. Since the timeline for this project was quite short (a single semester), we decided to select conductivity as the parameter to test our prototype design on. After experimentally determining the voltage threshold between light and dark graywater, I helped design a circuit that interfaced with Labview and a normally open valve that would be able to open and close depending on the conductivity of the water.


  • Research
  • Prototyping
  • LabView
  • Circuit Design

Local impact

Though this project spanned just a semester of class and the final product we developed was still very technically early in its development, the application potential of this project earned my team and I 2nd place at the Duke Annual Innovations Awards in 2012.


Global Impact

Daily, each person uses roughly 30 gallons of graywater. For a four-person household, that's 120 gallons per day and 3600 gallons per month per household of graywater. If we could get back just 50% of that, it would provide savings of roughly 21,000 gallons per year for a household of four people. This project intends to use the Duke SmartHome as a case study to develop a prototype that can aid in water conservation. The scope could later be expanded to implement this product in residential homes.


What this project means to me

As one of my first idea-to-prototype projects in college, this project taught me several valuable lessons:

1) Thorough assessment and planning of available resources (material and faculty support) for all phases of the project is key. We spent so much time focusing on researching details for the full-scale product, that we did not properly allocate time and resources to developing our prototype.

 2) There is also a fine line between thorough research and initiating the prototype/design iteration cycle too late. We should have narrowed the scope of our project at an earlier stage to allow for both a thorough assessment of resources and enough time for prototype and design iteration. 

The interdisciplinary nature of the project played a significant role in the learning process. We discussed and learned from professors from mechanical, electrical and environmental engineering departments. It was exciting to combine our expertise with areas we were unfamiliar with to develop the system. In retrospect, this project was indicative of a 'real-life' engineering challenge.