5! Is that correct? It can’t be that many…
In the book, Green Intentions, author Brett Wills discusses ways to reduce different environmental impacts by understanding the value stream of those processes within a business.
Under the topic of water reduction, he explains how to estimate the amount of water coming from various sources. After you count up the number of urinals and toilets, and record the gallons per flush (gpf) for each device, you should multiply the number of employees by 5, to estimate water usage. 5? That seemed extremely high to me, don’t you think?
So of course, I needed to do my own research to see if that is true. Here is what I found…
- 5.2 (Home Water Works)
- 3-4 in an office setting (men: 1 toilet and 3 urinal flushes, women: 3 toilet flushes; Delta Faucets)
- 5 as default (WECalc pg. 14)
- 4 (City of Tampa)
- 4 (Lawrence Berkeley Laboratory)
- 5 (article)
The last article actually references a study from AWWARF (now Water Research Foundation). I couldn’t find the original study, but I’m still looking for it. If you have something better, please let us know.
It seems like others are saying the same thing, and 5 is not far off. Many of these numbers are a daily toilet use, not separated by office and home. Only a couple of them break out the number by toilet and urinals. Here is my recommendation, for those trying to estimate water usage in a company.
- For urinals, use 3 flushes per office day per male employee
- For toilets, use 1 flush per male employee, and 4 flushes per female employee
This will put it at 4 total flushes per employee per workday.
So let’s show how this information might look in a spreadsheet. Let’s look at a company with 110 females and 95 males (205 employees), that pays $0.02 per gallon of water. What is the estimated cost of the urinals and toilets? This information could be used to determine payback on installing low flow toilets.
The estimated employees per device is based on the number of males and females and the percent of each device type, and assumes that each employee has an equal chance of visiting each device. If you want to get more specific, you might look at the breakdown by area (especially in larger buildings). So if you look at the urinals, there are 4 of the 2.5 gpf model, and 2 of the 1.0 gpf model. Since 67% (4 of the 6) urinals are 2.5 gpf, we calculate that 67% of the males will use it (63 out of 95 males).
Here is a link to a simple spreadsheet to get you started. Feel free to modify as needed.
Do you have a different approach? Please share!