4.5 Global use of Water

 

Figure 4.5.1 Global water by sector use since 1900

Figure 4.5.1 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

As mentioned in the first chapter, water use has increased exponentially over the last century. This is due not only to an increase in population and their direct water need, but also that population's associated consumption of food and manufactured goods which both consume water.

“During the last 50 years water use worldwide has grown fourfold now accounting for roughly 10% of total river and groundwater flow from land to sea globally” [see reference 17]

Figure 4.5.2 Global freshwater use by sector [see reference 18,19]

Figure 4.5.2 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

 

Figure 4.5.3 Water use by sector for a selection of countries [see reference 20,21]

Figure 4.5.3 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

Of the freshwater that is withdrawn for human use, in the industrial world, the bulk of water is used for industry. In developing countries the bulk is used for agriculture and in places like Afghanistan and Nepal, this is 99%. In all countries, domestic use is a small, but important part.

Worldwide the biggest use of water by far is agriculture. We will now look into more detail at what this water is used for in agriculture, then manufacturing and finally breaking down domestic use in the UK.

Agricultural Water Use

Figure 4.5.4 Use of water in agriculture

Figure 4.5.4 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

As the human population increases, there is growing concern that there won’t be sufficient water to grow the food required. As the figure shows, meat takes much more water to produce than cereals, and a steady increase in meat consumption has increased worldwide water stress. [see reference 22]

Table 4.5.1 Water required per kg of a variety of food

Type of Food	Water required per kg
Beef	15,000 to 70,000 litres per kg [see reference 23]
Chicken	3,000 to 6,000 litres per kg [see reference 23]
1kg Rice	4500 litres per kg
1kg Wheat	1000 litres per kg
1kg Sugar Beet	1000 litres per kg
1kg Potatoes	550 litres per kg

Sustainable food production will be covered in more depth in the next chapter but it is important to grasp at this stage the direct link between food and water, and the world reliance on both.

Industrial Water Use

Manufacturing processes of various types often require large amounts of water. In many cases these processes were developed at a time when water scarcity was less realised than it now is. Water conservation measures taken by industry can be improved with the development of new equipment and processes that require less water.

Figure 4.5.5 Water required for selection of manufacturing processes

Figure 4.4.1 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

Table 4.5.2 Water use of various manufacturing processes [see reference 24]

 

1 litre beer	8 litres of water
1kg paper	15-40 litres of water
1 kg bricks	1-2 litres of water
1kg steel	5-200 litres of water
1kg aluminium	1500 litres of water
1kg refined crude oil	1500 litres of water
1kg synthetic rubber	3000 litres of water
1kg fertiliser	600 litres of water

Much additional water is used in the process of manufacture for non-invasive processes such as cooling. While this does not necessarily greatly reduce river flow, if that is the source, it can result in changes to the river’s ecological system. Downstream of a warm water discharge, the change in river water temperature may encourage growth of algal blooms which can suffocate other flora and fauna inhabitants.

Domestic Water Use

Figure 4.5.6 Domestic water use in the UK

Figure 4.4.1 sourced from The ImpEE Project, The Cambridge-MIT institute. The ImpEE wesbite is designed as an educational resource. It may be reproduced, modified and used freely for educational purposes
http://www-g.eng.cam.ac.uk/impee/?section=topics&topic=water&page=slideshow

Although domestic water use accounts for only a small fraction of the total, it is concentrated in urban areas where it may cause local problems. There are many ways in which domestic water use could be reduced at relatively small cost. Water pricing policies will become increasingly important. Public perception of water is based on price and availability.

Table 4.5.3 Domestic water use in the UK [see reference 24]

Flushing lavatory, per flush	6-22 litres
Bath	80-170 litres
Shower, per minute	5-10 litres
Automatic washing machine, per load	70-110 litres
Dishwasher load	55 litres
Watering garden, 1hr	1000-1300 litres

Table 4.5.3 sourced from The Open University under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence
http://www.open.edu/openlearn/science-maths-technology/science/physics-and-astronomy/physics/renewable-energy

All water that is piped into homes in the UK is treated to very high EU quality standards. Much of the water we use domestically is consumed in non-potable uses such as gardening and flushing toilets. Only uses including drinking, cooking and for baths and showers need to be potable for health reasons. These uses account for only around one third of total supply. see reference [25]

Note: Dishwasher figures vary depending on the type of dishwasher. Some estimates are as low as 12-16 litres per load, which is substantially less than washing by hand [30], although energy considerations must also be taken into account when comparing the two.