About A Minute’s Worth Of Hot Water Is Lost Every Time A Shower Is Taken

Behavioral waste occurs when bathers use their time comfortably and efficiently while waiting for hot water to reach the shower. It is defined by the period of time they continue to remain away from the shower after bathing temperature water has arrived. Because its volume will vary based on a showerhead’s flow rate, behavioral waste is most appropriately expressed in time. Analysis of recent data collected by Lawrence Berkeley National Lab (LBNL) in the greater San Francisco Bay Area combined LBNL analysis of the 1999 REUWS (Residential End Uses of Water Study)
suggests that behavioral waste exists within a 38 – 56 second range.

The low end of the range, 38 seconds, is derived from the analysis of field data collected by an LBNL monitoring system in December 2013.

The high end of the behavioral waste range, 56 seconds, is computed by applying the results from the December 2013 LBNL field data to conclusions drawn from a 2004 LBNL paper that analyzed approximately 26,000 shower events within the 1999 REUWS database.

Given the data’s conservative nature (it was predominantly collected in areas with “greener” behaviors than typical) it’s reasonable to conclude that about a minute’s worth of hot water is inadvertently wasted every time a shower is taken and behavioral waste will vary from region to region.





That’s Several Gallons Lost Per Shower

Behavioral waste must ultimately be converted to gallons for the purpose of making water and energy savings calculations. When making this conversion a showerhead’s flow rate and other factors must be considered. Given these variables, behavioral waste can range from 1.7 to 3.4 gallons to as much as 2.5 to 4.9 gallons per shower (see matrix below).





“Behavioral waste occurs when bathers use their time comfortably and efficiently while waiting for hot water to reach the shower. Activities include brushing teeth, using the washroom, picking out clothes, drinking coffee …”


Primary Analysis Method

Applying the fundamentals of a method developed by Lawrence Berkeley National Laboratory, Evolve Technologies was able to analyze the shower events captured by the LBNL monitoring system in December 2013. The analysis method consists of plotting the time, temperature and flow rate data collected by the system at each bathroom’s showerhead. Once the data is plotted it is possible to identify and quantify the unique components of each shower event.

Structural waste occurs from the point at which the shower is turned on to the point at which the water approaches bathing temperature (95F/35C).

Behavioral waste occurs from the point at which the shower approaches bathing temperature (95F/35C) to the point at which the user enters the shower, the entry point. The entry point is indicated by a rapid reduction and subsequent stabilization of the shower’s temperature after the shower’s peak temperature has been achieved. It is caused by the typical user behavior of turning the shower to full hot to speed the shower’s warm up and then adjusting to a comfortable bathing temperature upon entering the shower.

Bathing use occurs from the entry point to the end of the bather’s shower. It is the hot water that’s actually used for bathing.


“In General, it appears as if the desire by users to multitask as part of their shower warm-up routine is strong and established habits may be difficult to break regardless of how quickly hot water arrives to the point-of-use.”


Fast Hot Water Delivery Significantly
Increases Behavioral Waste

It is commonly believed that reducing structural waste by delivering hot water quickly to the point of use will produce a behavior change in bathers resulting in a significant reduction in behavioral waste. However, analysis of the LBNL data suggests that there is no correlation between low structural waste and reduced behavioral waste. In fact, bathrooms with consistently fast hot water delivery times (20 seconds or less) showed significantly more behavioral waste than average.

Specifically 50% of the bathrooms monitored by the LBNL system exhibited consistently fast hot water delivery, yet those bathrooms also exhibited 32% more behavioral waste than average.

Rather than significantly reducing the total amount of warm-up waste (structural waste + behavioral waste), fast hot water delivery primarily increased the percentage of behavioral waste within a relatively consistent warm-up waste volume.

The ShowerStart TSV produced by Evolve Technologies LLC is an effective tool for eliminating behavioral waste without requiring behavior change. As such, it is essential for guaranteeing the deemed savings commonly attributed to efficient plumbing configurations and products capable of reducing structural waste i.e. hot water recirculation systems.

Behavioral Waste Table

Behavioral waste is an activity driven event and the volume of hot water wasted will vary depending upon multiple factors. The table below calculates behavioral waste volumes based on showerhead flow rate, time spent away from the shower and includes an incremental adjustment for tub spout warm ups. “Greener” regions of the country will likely skew towards towards the lower end of the scale, while other regions will likely fall in the middle to higher end.

Behavioral Waste Matrix