Closed system: water

gio_waterSometime ago I wrote about the need to consider the planet as a closed system, i.e. a system to which no new mass is being added, other than the occasional meteor from space [see my posts ‘Closed systems in nature?’ and ‘Open-world mind-set’ on December 21st, 2012 and January 4th, 2013, respectively].  This closed system approach applies to water.  The total amount of water on the planet does not change and it has been moving around the hydrologic cycle for thousands of years.  Mankind interacts with this cycle changing the chemistry, usefulness and availability of water.  All of us contribute to these changes in a small way but 6.5 billion of us make a big impact.

Most of us are aware of pollution to rivers and groundwater caused by use of fertilizers and pesticides.  We are perhaps less aware that removing groundwater for irrigation, industrial processes and domestic consumption can reduce water pressure underground in coastal regions causing saltwater to percolate and mix with freshwater reserves.  Or that discharges from desalination plants increases the local salinity of seawater while carbon emissions in the atmosphere is sequestered by the oceans raising water acidity levels.  All of these effects can damage ecosystems.

80% of available freshwater resources in the world are used to grow food.  Yet, we also need it in huge quantities for industrial processes, for instance it requires 10 litres of water to make a sheet of paper and 200 litres to make one kilogram of plastic.  Just as in energy consumption, there are huge global variations in daily domestic consumption per capita from 778 litres in Canada, 139 litres in the UK and India to 95 litres in China.

So, in addition to thinking about energy consumption when designing products and services, engineers need to think about water requirements since although there is a renewable supply it is not  infinite or even constant.

The data above was taken from ‘Water: A Global Innovation Outlook Report’ available at

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