sustain

An interesting report on the connection between energy usage and water in Energy-water Nexus: Energy Use in the Municipal, Industrial, and Agricultural Water Sectors by Gweneth M. Thirlwell, Chandra A. Madramootoo and Isobel W. Heathcote presented at the Canada – US Water Conference in Washington D.C. on October 02, 2007.

A quick culling of interesting points/results:

Motivation

Water is essential to many activities in the home including washing, cleaning, cooking, drinking and recreation. Industrial processes rely on water for cooling, chemical solvents, cleaning, just to name a few. Forty percent of the worlds’ food is produced from irrigated lands [1]. However, much of this would not be possible without energy; which is a critical input to pump, move, and treat the water required by municipalities, industries and agriculture. Ironically, however, much of this energy would not be available without water to turn turbines, wash inputs, or cool equipment. Thus in many cases use of one resource is inextricably linked to use of the other – hence, the energy-water nexus.

Statistics on Electricity Generation

While the focus of this paper is on the energy required to supply water, is it interesting to note that one of the largest uses of water is electricity production. Water is used in thermal, nuclear, and hydroelectric power generation. To produce one kilowatt-hour of electricity requires 140 litres of water for fossil fuels and 205 litres for nuclear power plants [8]. Every year almost twothirds of generated power in Canada is produced via hydroelectric generation [9] (figure 2). This electricity is then used to treat, pump, move, and heat water (among other things). Thus, the nexus comes full circle; water is used to produce the electricity which is used to consume water.

Statistics on Water Use

We consume more water than most other countries: Americans ranking first and Canadians ranking fourth highest consumers of water out of 29 countries in the Organisation for Economic Cooperation and Development (OECD) [10]. Canada’s annual per capita use sits around 1430 m3 while the United States’ is approximately 1730 m3. Canada’s per capita water consumption is 65% higher than the OECD average and overall use has increased by 25.7% since 1980 [10]. While some municipalities have been successful in curtailing water use, overall residential water use increased by 21% during the 1990s [11]. In part, this is because of demographics: our growing population places steadily increasing demands on water supplies, even if per-capita consumption is stable or decreases.

Standard of Living and Water Use

Based on the example set by European countries, it is possible to have a high standard of living and consume less water. The average Dane uses eight times less water than a Canadian [10]. And yet we chronically over-use water. There are several reasons for this; having some of the lowest water costs in the industrialized world has certainly not encouraged us to curtail our water use [11]. Indeed, many municipalities do not require water metering, or even charge less per cubic meter as consumption increases (declining block pricing), so consumers are not even aware of the costs of their consumption. In part, this may be because Canada has a long held the belief that it is a water abundant nation, and therefore does not need to worry about consumption rates[13]. This is reflected in Canadian policy and consequently supply-side driven management of water resources[11, 13]. However, we are finally beginning to realize that we can no longer afford such careless attitudes towards our resource use.

Reducing Water and Energy Use

For sanitary sewers and associated treatment plant, such reductions will normally be achieved by demand-side reductions, especially residential and industrial water conservation. For storm and to some extent combined sewers, energy use reductions can be achieved by technologies that detain flows and encourage infiltration to groundwaters, and which provide some degree of treatment. Many technologies are available for this purpose, including infiltration ponds, trenches, constructed wetlands; and similar structures; rain gardens (lot level infiltration structures); rain barrels; green roofs; narrower roads bordered by permeable surfaces such as grass or ornamental planting; and so on. Further reductions could be achieved by implementing water reuse and recycling strategies.

The Municipal Sector

The largest uses of municipal water are residential (52%) and leakages (13%). Thus, tackling these uses would target 65% of water use, and the incumbent energy use. Many low-cost, easilyimplemented technologies have been developed in the past two decades [23]. Old model toilets used 6 gallons per flush, while new models use only 1.6 gallons, and composting toilets do not require flushing at all [12]. Other low-cost technologies include low-flow shower heads and faucet aerators. Additionally, water efficient appliances also help to reduce water use and ultimately energy use.

One study in California by the Pacific Institute shows that “total commercial, industrial, residential, and institutional water use could be cut by at least 30% using available “off-theshelf” technologies” [12], ultimately leading to reduced energy use for supplying and treating water. In some cases, this reduces the strain on urban water infrastructure and avoids costly upgrades and expansions as population grows [24]. The city of Cochrane, Alberta, reduced water consumption by 15% by giving away toilet dams flow showerheads, and faucet aerators. This reduction enabled the city to defer the construction of a multimillion-dollar pipeline [24].