I’ve been asked a number of times to include water on my greenhouse gas spreadsheet, and now have the numbers to do so. Energy demands for water use are significant. Unfortunately, most of the water we consume never appears on our home water bill. Our bill doesn’t show us water use for eating and showering elsewhere, or for water use in agriculture or manufacturing—1 kg of cotton requires 2900 gallons of water (global average), a t-shirt 715 gallons. In many areas of the world, including California and the US, people consume fossil water (groundwater), and replacement will come from higher emissions desalination.
According to California Energy Commission (pdf), 19% of CA use of electricity, 32% of natural gas, and 88 million gallons of diesel goes to water supply and treatment, and wastewater treatment, for all uses. Energy for residential water, at least in California, comes mainly from electricity.
So how much of my annual electricity usage belongs to the category water use? What percentage of my annual water use appears on my home water bill?
Electricity for home water use
The US average, according to Energy Star’s Water/Wastewater Focus: A National, Collaborative Approach to Enhance Energy Performance within Municipal Facilities (pdf), is 1.5 kWh/thousand gallons (kgal) drinking water, and another 1.2 kWh/kgal sewage. (Typically about half of water goes to sewage.) Variations can be large—in my water district, East Bay Municipal Water District (pdf), water flows downhill, and the electricity use is 1.25 kWh/kgal, with another 1.5 kWh/kgal sewage. EBMUD estimates that a person halfway uphill in Berkeley/Oakland uses 25 kWh/year more than a person in the flats (assumes 50 gallons/day, personal communication David Beyer, EBMUD). Getting water to southern CA requires more pumping, and electricity costs are higher, 6.4 kWh/kgal.
To calculate your energy use for water, for indoor and outdoor residential, plus some for work or school, restaurants, and the gym:
• Get your yearly water use from your bills. Multiply ccf (hundred cubic feet) by 748 to get gallons. Divide by 1,000 to get water consumption in kgal.
• Round up. My assumption is that everyone should round up by at least the larger of 10 gallons/day or 20%, to count water use outside the home, from vacations and toilets and restaurants and showers at the gym to the water use on veggies at the store, etc. People in apartments who use a lot of water outside the home may want to double what the bill tells you.
• To calculate wastewater use, multiply water consumption by a value between 0.4 (a high percentage of your water goes into the yard rather than wastewater) and 1 (apartment dweller).
• Multiply water use estimate by electricity use/kgal, and multiply wastewater estimate by electricity use/kgal.
• Divide by the size of household to get per capita electricity use.
Example
Family Ex’s bill says that the two residents use 100 gallons/day, or 36,500/year = 36.5 kgal/year.
The Exes eat out about 10 meals/week, and one goes to the gym a couple of times/week. They are away from home 20 days/year. Add 40%, to get 51 kgal/year. (Your guess is probably better than mine.) If the Exes are typical, wastewater will be half that, or 26 kgal/year.
Multiply water use by 1.5 kWh/kgal, and wastewater by 1.2 kWh/kgal. (US values)
Electricity use: 51 (1.5) + 26 (1.2) = 110 kWh
Per capita electricity associated with water use for the two Exes is about 55 kWh/year.
Reducing water use
The Exes can reduce water use in a number of ways—see your local water utility for recommendations. Here is EBMUD’s watersmart page and their information on gray water. The NY Times describes the work of Greywater Guerrillas, a group that feels that the CA code is too complex, and expensive, in The Dirty Water Underground.
gray water idea from the greywater guerrillas
Xeriscaping can add beauty as well as reduce water use.
Suggestions I don’t always see on lists of ways to save energy for water:
• cook with less water—boil only as much as you need.
• turn water on and off while washing dishes. Run water continuously and you’ll use several times as much water.
More information
• The energy to heat water is not included, but is significant. If you heat water with natural gas, then 34 gallons of hot water for an entire clothes wash cycle requires 0.34 therms. Warm water has about half the energy requirements of hot water. Compare this to the energy cost of operating the washer, 0.3 kWh electricity. A gas dryer might use 0.17 therm, plus 0.5 kWh electricity, and an electric dryer 3.3 kWh. One reason so many utilities give rebates on water efficient washers is to reduce hot water use.
Pardee Reservoir is part of the EBMUD water system.
• Actual water use is MUCH greater than our bill tells us. According to Energy and Air Emission Effects of Water Supply (pdf), typical water use is 86 kgal/year, more than 230 gallons/day: this counts commercial and educational establishments, industry, parks, swimming pools, etc.
We in EBMUD’s service area use 130 gallons/person/day. These numbers are down because we are responding to the drought, and because industry has moved away. Numbers will stay down because we have adopted drought behavior. (personal communication Michelle Blackwell, EBMUD)
In numbers that have surely decreased—Californians have been changing their behavior, water use has becomes a tad bit more efficient, and industry has declined in both real and per capita terms—estimated CA water use in 2000 was 7 million acre feet for 34 million people, 180 gallons per day (gpd) per person, 67 kgal/year.
By sector in CA:
indoor residential: 22 kgal/year, 60 gpd
outdoor residential: estimates range from 9.4 kgal/year, 26 gpd to twice as much
commercial/institutional: 18 kgal/year, 41 gpd
industrial: 6.4 kgal/year, 17 gpd
unaccounted for: 6.7 kgal/year, 17 gpd
Waste Not, Want Not: The Potential for Urban Water Conservation in California (pdf)
For US numbers, see USGS Estimated Use of Water in the United States in 2000 (Notes: US population in 2000 was 281 million. Water used by power plants is for the most part returned, though at a higher temperature.)
irrigation: 490 gpd per person
public-supplied for 85% of the population: 180 gpd
self-supplied industrial: 70 gpd
self-supplied domestic, livestock, aquaculture, and mining: 46 gpd
• In addition to greenhouse gases, each 1000 gallons CA water use (pdf) produces 7.2 g NOx, 1.5 g particulate matter, and 11 g SOx. US averages are about 60% worse for greenhouse gas emissions, twice as bad for NOx, 10x as bad for particulate matter, and 2.5x as bad for SOx. This is due primarily to a different mix of sources of electricity.
• Desalination will become increasingly important in CA (and elsewhere) as population increases from 37 million today to 46.5 million by 2030 (US Census).
Drinking water scarcity is an issue in many parts of the world. By 2025, 1.8 billion people will be living in areas likely to experience absolute water scarcity. More than 40% of the world’s population may face serious water shortages if they must rely solely on locally available freshwater. Some of these places experience scarcity due to climate and others because infrastructure is unavailable; however, in some places, both issues are problematic.
Energy and Air Emission Effects of Water Supply (pdf)
Desalination will increase energy use/kgal by as little as 50% or as much as 140%.
• In dry states, water use also contributes indirectly to climate change, and ecosystem damage, because competition between ecosystem needs and human needs almost always lead to less productive ecosystems, and reduced carbon dioxide taken out of the atmosphere.
