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).

 

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.

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.

• Explore the impact of improving the efficiency of the plumbing fixtures specified on reducing water use.
• Determine which plumbing fixtures should be changed to reduce indoor water use by 20 percent and earn 1 LEED point.
• Investigate whether it is possible to reduce indoor water use by 30 percent (and earn another LEED point) by improving the efficiency of additional fixtures.

Figure 3.3.2 -  Indoor plumbing fixture summary in Green Building Studio

• Evaluate the feasibility of using rainwater harvesting to further reduce water consumption and maximize LEED water efficiency points.
• Create an Autodesk^®  Revit^®  schedule to tabulate the total roof area available on the school campus.Use Green Building Studio to determine the rainwater harvesting area required to collect enough water to reduce water consumption by 50 percent and earn one LEED point for Innovative Wastewater Technologies.
• Continue working with Green Building Studio to determine the rainwater harvesting area required to reduce water consumption by 100 percent and earn a second LEED point for exemplary performance in Innovative Wastewater Technologies.
• Determine which roof surfaces in the BIM model are the best candidates for rainwater collection to provide the needed rainwater harvesting area.

Figure 3.3.4 -  Summary of LEED Water Efficiency Credits in Green Building Studio

High-efficiency plumbing fixtures typically bring a sizable reduction in water use at a small cost. The initial cost to purchase these fixtures is often slightly higher than standard fixtures, but this one-time cost is quickly offset by the continuous water savings for years to come.

High-efficiency plumbing fixtures are usually no more expensive to install than standard fixtures. The differences are typically limited to the flush valve mechanism. No additional piping or preparation is needed.

Several types of high-efficiency toilets are available. Low-flow toilets that consume less water with each flush have been available for many years. Dual-flush toilets (which offer two flushing modes—less water for liquid waste and more water for solid waste) have been used around the world for many years and are now being introduced in the United States.

Urinals with low-flow valves are typically installed in most new public restrooms to conserve water. Waterless urinals have been introduced and are becoming more common, but are not yet widely used.

Low-flow shower heads offer a quick-and-easy strategy for dramatically reducing the water consumed during a typical shower session. Low-flow mixing valves and timers are also available, but they are much less common. 

A related issue that affects water consumption is how the water is heated. When water is heated at a central tank and piped to a remote shower, much water is consumed as people run the shower to clear the cold water in the pipes and wait for the hot water to be delivered. Tankless water heater systems help to reduce this water waste by instantly heating the water near the shower on demand. 

Recirculating hot water systems can also help reduce water waste by pumping hot water through the pipes, so hot water is always nearby. Of course, the energy cost of continually heating the water and pumping it through the pipes should also be factored when considering this strategy.

Low-flow faucet heads are available but not commonly used. More attention is usually focused on the faucet controls to limit the duration that the water is running.

Automatic sensors can dramatically reduce the water used at a lavatory sink by stopping the water flow when nothing is using it. When hands are detected by the sensor, water flows; when hands are no longer detected, water stops. Sensors are commonly used in new public restrooms but are far less common in residential settings.

Another low-tech approach with a similar effect is spring-loaded faucet valves that cut off the water after a fixed time period has elapsed.

Greywater that can be reused is typically produced by lavatory sinks, showers, washing machines, and other devices that drain water that does not contain any sanitary waste.

Greywater is often used for flushing toilets and urinals and landscape irrigation.

To implement are greywater system, a secondary set of drain pipes must be used to divert water from greywater-producing fixtures into a collection system (rather than into the sewer system). A secondary set of water supply pipes must also be provided to transfer the greywater to the fixtures and devices that will use it.

Where rainwater is not plentiful, groundwater collection systems of wells and pumps offer another net-zero source of water.

Rainwater can also be collected from ground surfaces and landscaping. For example, the runoff from a paved parking lot or landscaped area can easily be diverted to a cistern (rather than flowing into the storm sewer system). Rainwater collection systems can also be installed under grassy playing fields, which typically provide a large, relatively unobstructed collection area.

The estimated water usage when using fixtures that meet the standard building code minimal requirements.

Innovative design strategies that reduce the amount of water that must be supplied by local utilities. These measures can include collecting water from on-site sources as well as designing features and specifying systems that do not require off-site water.

Recyclable water collected from sinks, showers, washing machines, and fixtures that do not introduce any sanitary waste. Greywater is typically used for irrigation as well as flushing toilets and urinals.

Collecting, storing, and using the rainwater that naturally falls on a building or site. Rainwater harvesting is an example of a net-zero measure, using water from an on-site source (that would otherwise be wasted) to reduce the water consumed from local utilities.