Water Use and Collection

BIM for Architecture, Engineering, and Construction Curriculum


In this lesson, students learn how to estimate the amount of water a building’s users and fixtures will consume and the percentage of this water demand that can be met sustainably by collecting rainwater.

Using a school campus composed of classroom units designed in the previous lessons as an example, students use the tools in Autodesk® Green Building Studio® software to estimate the water demand by considering the usage patterns and the fixture efficiency. 

Next, they explore the potential for using an example of a net-zero measure—rainwater harvesting—to collect water to offset the water consumed by the users and fixtures. 

Finally, student evaluate the potential for earning LEED® points for by reducing water consumption through improved fixture efficiency as well as net-zero measures and recommend a strategy that balances these various design options.

Estimating the Water Demand Baseline

We can use the tools in Green Building Studio to estimate the total water demand created by the usage patterns and performance characteristics of the fixtures in our building model. We can start by considering the water used by each of the plumbing fixtures, then tabulate the data to estimate the total water demand. 

The water used by each of the plumbing fixtures depends on several factors:

  • The flow characteristics of the fixture—the amount of water consumed by each use.
  • The usage pattern—the estimated number of uses based on the number of building occupants, the building area provided, and the building type (for example, office versus school). Weekday usage is often quite different than weekend usage, especially for buildings that are used primarily on weekdays (such as schools).

(slider Plumbing Fixture Efficiency}

Most plumbing fixture manufacturers have introduced high-performance, low-flow versions of their products that allow you to create more efficient, sustainable designs. So as you place plumbing components in your model, you can consider and specify the types of fixtures to be used:

  • Standard fixtures that meet the minimum requirements specified by the applicable building codes
  • High-performance, low-flow fixtures that exceed the minimum requirements and reduce water use. 

While high-performance fixtures may be more expensive to purchase, the additional investment is typically recovered quickly through their improved efficiency.

Offsetting Water Use Through Net-Zero Measures

After reducing the estimated water use of a building through improved efficiency (for example, using high-performance fixtures), we can further reduce the water that will be needed from local utilities by finding ways to collect or reuse water on-site. 

An effective strategy for locations and climates with significant rainfall is to collect and use rainwater to meet a part of the demand. Rainwater is often:

  • Collected on roof surfaces
  • Diverted to filtration systems and storage tanks
  • Pumped to supply the water used by some plumbing fixtures 

Other net-zero strategies to consider include:

  • Use greywater systems to recycle water that can be used to flush sanitary fixtures or irrigate the landscaping.
  • Plant native vegetation that does not require irrigation.
  • Install waterless fixtures.

Many design teams set a design goal of meeting a specific percentage of a building’s estimated water demand through renewable sources, such as rainwater collection. Using the results of iterative analyses, design teams can decide on the optimal amount of rainwater collection area and compare the effects of various alternatives to meet their design goals.

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