I got a start on figuring out exactly how much petroleum depletion will affect water use and availability today reading Yes! Magazine's issue 54 "Water Solutions Issue". Sandra Postel makes a good point in the article "Will There be Enough?" that will there is quite a bit of attention on fossil fuel depletion, water waste and contamination is a far more pressing problem:
"In answer to the climate crisis, the economy will need to move away from fossil fuels toward solar, wind and other non-carbon energy sources. But there is no transitioning away from water. Water has no substitutes. And unlike oil and coal, water is much more than a commodity: It is the basis of life."
Also in the issue, they state that the average American household of four uses 400 gallons of water per day. This isn't hard to believe once you start running the numbers on individual water uses each day. For example, a household in Phoenix with a backyard pool loses 50 gallons a day to evaporation alone (if the pool is left uncovered as most are). A single load of laundry is 40 gallons, and each family member's shower is around 20 gallons each morning. A simple exercise of tracking water use throughout a day has gone a long way for my understanding of water use, and could make a big difference in watershed-wide water use and waste if more people understand how much water they are using for what.
Domestic water use however, is only one slice of the pie of water use in the nation. Minnesota uses 1,404 Billion Gallons of water each year. Of this only 15% (217 billion gallons) is domestic water use. The biggest user is power generation, at 60% of water use. "About 90 percent of US electricity comes from thermoelectric power: turning water into steam by burning coal, natural gas, or oil, or using the heat from nuclear reations." A lot of water is required for the production of electricity, both in steam generation and for use in cooling machinery to prevent overheating.
Ironically, not only is water needed to produce electricity, energy is also needed to transport the water from place to place. 1.6 kWh is needed to transport one cubic meter of water from the Colorado River to Southern California. That equals 6 watts per gallon. "the energy required to provide drinking water to a typical southern California home can rank third behind that required to run the air conditioner and refrigerator. An even more energy intensive method of 'producing water' is desalination. To convert salt water to drinkable water takes 2 kWh per cubic meter or 7.6 watts/gallon. While this might not seem like much, with 400 gallons used a day, at 6 watts per gallon that is a total of 2,400 watts or 2.4 kWh per day just for water transport.
This all makes collecting water right where it is delivered to you via rainfall much more appealing. Why not take advantage of the 'free' distribution processes of nature? Collecting water on your roof is not only very clean (if filtered for sediments) but also uses NO energy to transport.
While the 6 watt number is for southern California for the sake of comparison while I dig for Minnesota-specific numbers I would be using a total of 324 watts of energy every day to provide the 54 gallons/day I was using before this project. During the project (if I were actually collecting the 15 gallons average rainfall from my roof) I am using no energy, and only 27% of the water.
Even more shocking is the statistics outlined in Hoakstra and Chapagin’s article "Water footprints of nations, 2006". "One cup of coffee requires for instance 1401 gallons of water in average, one hamburger 24,001 and one cotton T-shirt 20,001". The 400 gallons of water used in an average household each day could be saved by skipping out on ONE quarter-pound hamburger. The following table of water use for various products is from Hoekstra and Chapagain’s article, found online here: http://www.waterfootprint. org/Reports/Hoakstra_ and_Chapagain _2006.pdf
Table 2 Global average virtualwater content of some selected products, per unit of product
Product Virtual water content (litres)
1 glass of beer (250 ml) 75
1 glass of milk (200 ml) 200
1 cup of coffee (125 ml) 140
1 cup of tea (250 ml) 35
1 slice of bread (30 g) 40
1 slice of bread (30 g) with cheese(10 g) 90
1 potato (100 g) 25
1 apple (100 g) 70
1 cotton T-shirt (250 g) 2000
1 sheet of A4-paper (80 g/m2) 10
1 glass of wine (125 ml) 120
1 glass of apple juice (200 ml) 190
1 glass of orange juice (200 ml) 170
1 egg (40 g) 135
1 hamburger (150 g) 2400
1 tomato (70 g) 13
1 orange (100 g) 50
1 pair of shoes (bovine leather) 8000
1 microchip (2 g) 32