figuring out how much water I directly use

nature cover 3_20_08 ==> This weekend, I was reading Nature’s latest issue, on the world’s water problems. I learned just now that Saturday was “World Water Day”, so that probably explains the timing of the issue. I also found it an interesting timing to encounter this, since I’ve recently talked with several friends about rising water challenges. Several of the Nature articles cite large figures for water, figures that I had no direct way to relate to. So I decided to measure my average water use. I figured I would learn more about how I use resources that I normally take for granted, and to get familiar with larger quantities of water that nation- and Earth-level reports refer to.

My objective was to estimate my “direct” water usage. So I didn’t include major “indirect” uses of water, such as the amount of water I’ve “used” in purchasing food that required much water to generate. And I’m not including my use of electricity that is backed in part by nuclear-derived energy, which requires considerable amounts of water for cooling. (I’m looking forward to investigating these water uses in future posts)

So this was pretty straightforward. To get total volume of water used in a day, I had to get the volume flow rate of all my sources of water, multiplied by the duration I use each. I then accounted for activities that are daily, while others are only a few times a month (eg, doing the laundry), and then summed these. Below are the results.

I was most surprised to see how much using the bathroom and kitchen faucets, contributed to nearly half of my daily water consumption. I hadn’t thought about it much before, and had always assumed using the shower would dominate water use from faucets. (click for large version)

water breakdown

Some of my key assumptions / measurements:

  • Shower once daily, 10 minutes, measured flow rate of 7.4 L/min (I used a stop-watch and the pitcher from our blender).
  • Bathroom faucet – use 3 times daily for 3 minutes each (washing hands after work, shaving, washing face before bed), measured flow rate of 4.2 L/min
  • Kitchen sink faucet – use 3 times daily for 3 minutes each (rinsing dishes, washing hands, rinsing dishes)
  • Toilet – flush twice daily, manufacturer-specified flush volume of 6 L
  • Clothes-washing machine – use once every 10 days, on medium setting. Estimated water volume used, by eyeballing water fill-height on medium cycle, and measuring the dimensions of the cylindrical compartment.
  • Dishwasher – use once every 5 days (assuming I’m living solo, since I’m calculating on a per-person basis), with estimated 10 gallons per run (38L; estimated as the upper range of average dishwasher water use, from the Soap and Detergent Association, 2000; interesting, short article on dishwasher history and water useage here)
  • Kitchen sink (drinking water) — estimated 3 liters a day used for coffee, tea, and water.

When I multiply these volumes to get a yearly estimate, I calculate I directly use ~70,000 L of water, or 70 cubic meters. That seems low, given that the average person is expected to need 1,700 cubic meters of water annually, according to several of the Nature articles. So, assuming I didn’t make some buried arithmetical error, that means that most of the water I use is for food and energy. This seems likely, since, again according to statistics cited in the Nature articles, it requires 15,500 litres of water to produce 1 kilogram of industrial-quality beef. That’s approximately three 12-oz steaks. At a gross qualitative level, this seems to make sense, given the large amount of plant-derived animal feed that must be grown, in order to feed livestock.

But as with the daily-use numbers above, I don’t have enough of an intuitive understanding, to know whether 15,500 liters of water for 3 steaks seems reasonable or not. I’ll look forward to digging into that next :). I’m also wondering whether there are personal water-use measuring tools on the web, to help people learn about their water use, and at first googling I don’t see evidence of one…

Hold that, found one!

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2 comments

  1. […] after my last post on water, which was a happily received awakening about how much water I used — nearly 200 liters a […]

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  2. […] this year, Andrew measured his average water use and found it ranged from 100 – 200 L/day. To illustrate the water intensity in making food products, Rijsberman described the […]

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