W03: Water Efficient Water Closets – Above Green

Requirement Summary

This measure can be claimed when the water closets in all bathrooms of the building have a dual flush mechanism, or if they have an efficient single flush or flush valve. It is required that the actual flush rate of water closets be entered in EDGE in all cases, irrespective of the value.

Intention

Installing dual flush water closets helps to reduce the water used for flushing by providing a reduced flush option when a full flush is not required. Installing a more water efficient single flush water closet or flush valve similarly helps to reduce the water used to flush.

Approach/Methodologies

This measure will result in savings if the main flush is less than the base case in liters/flush and/or if the second flush is less than the base case in liters/flush. The default flush volumes for the improved case must be replaced with the actual values provided by the manufacturer.

In the case of a more efficient single flush system, select the Single flush/flush valve choice in EDGE. The actual flush value must be entered in the field for the volume of the flush. If the volumes of the flush vary across a project, a weighted average must be used. Multiple measurements must be made across a variety of locations and floors to come up with a weighted average.

Potential Technologies/Strategies

Dual-flush water closets have two flush levers where the smaller volume flush is recommended for liquid waste, and the higher volume flush for solid waste. The design team should be careful to select dual-flush water closets with clear intuitive controls, and a good flush performance rating. In some cases, dual-flush water closets can adversely increase the volume of water used if the method of use is not clear, or if they do not flush the waste adequately, requiring repeat flushes. The Environmental Protection Agency in the U.S. has a label, “WaterSense,” with tests for water efficiency and performance, for high-performance water closets. The EPA website is a useful reference to identify dual flush water closets which have low water use but equivalent flushing performance to water closets with higher flush volumes.

Relationship to Other Measures

This measure is not affected by any other measure. However, this measure impacts building energy consumption due to a change in the energy use of water pumps as the total volume of water pumped changes (this portion of the energy consumption is included within the Energy Use category “Other”).

Assumptions

The base case assumptions vary by location based on studies. Globally, the typical baseline is a flush volume of 8 liters. The improved case assumes a flush volume of 6 liters for the main flush and 3 liters for the reduced flush.

Compliance Guidance

Design Stage

Post-Construction

At the design stage, the following must be used to demonstrate compliance:

Plumbing drawings/specifications including make, model and flush volumes of water closet(s); and
Manufacturer’s data sheet for water closet(s) with information on the flush volume of the main and reduced flushes.

At the post-construction stage, the following must be used to demonstrate compliance:

Photographs of installed water closet(s); or
Purchase receipts and delivery note for water closet(s).