A single cup of coffee per day has reduced my hot water usage by 20.5% — it seems improbable that such a small amount of liquid could have such a large impact, but I have been taking careful notes and checked them twice: it’s true. Here’s how I figured this out.
My hot water usage is composed of a daily shower, a small amount to wash my face, and one quarter of the dishwasher usage, as I share with my family of four. All our clothes washing is in cold water.
As per an earlier post in which I measured the water usage of various low-flow shower heads and settled on the Oxygenics Elite 700. When on full-blast, it uses 1.6 gallons per minute (GPM); when the lever is turned to low it uses about 9/10ths GPM. I’ll typically turn it on high to get wet, shampoo and rinse my hair (50% of shower time), then turn it on low while I wash my face and body (30%), then on high to rinse off (20%), or 70% at 1.6 GPM, and 30% at 0.9 GPM. Because I have set my water heater to about 115 degrees, it’s almost or all hot water.
Our Energy Star dishwasher uses about 4 gallons per cycle, of which I account for 1 gallon per day.
So how does the coffee affect hot water usage? Since November I have been using the Shower Professor shower timer, and keeping track of my results. When I step in, I set the timer for 5 minutes. When I get out of bed in the morning and stumble into the shower, I often find that I’ll use the full five minutes, or even 15 seconds more. However, if I have had a cup of coffee before, I regularly complete the shower in under 4 minutes.
So to do the math:
Un-caffeinated: (((70% * 1.6 GPM) + (30% * 0.9 GPM)) * 5.25 minutes) + 1 gallon = 8.3 gallons
Caffeinated: (((70% * 1.6 GPM) + (30% * 0.9 GPM)) * 4.0 minutes) + 1 gallon = 6.6 gallons
Difference: (8.3 – 6.6)/8.3 = 20.5% reduction in hot water use when I have had coffee before taking a shower.
Unfortunately, I am not very good at making coffee until I have had a hot shower.
No, seriously, I take a shower about 20% faster if I am awake and aware.