Perhaps no resource integrates the damage upon the biosphere like water. Water is the great meeting point of chemistry, where things dissolve and enter food chains. Water therefore conveys the havoc wrecked by our activities upon the environment and ourselves.  Melted glaciers raise the sea levels, encroaching upon the land; carbon dioxide dissolves in water to produce ocean acidification; our fertilizers flow down the streams into the lakes and coastal waters to rob the aquatic life of oxygen; the salt from excessive irrigation poisons the soil; toxic mine tailings enter our rivers; ballast water introduces invasive species from the other side of the planet, decimating local ecosystems; greenhouse gases destabilize the climate, producing the two-edged sword of drought and flood, killing our crops and eroding our soil in turn; dirty water delivers disease to the disaster zones and the refugee camps, when humans are at their lowest ebb anyhow.

Water truly is the conveyer of bad news.  It is also essential for our survival. As the universal solvent, it is the solution space for biochemistry.  It acts as a temperature regulator, preventing sudden rises in our internal temperatures.  It cushions our organs from damage and dilutes our toxic nitrogenous waste as urine.   In many organisms it provides the mechanical support as a hydroskeleton. Humans are particularly vulnerable to dehydration, with symptoms becoming apparent when just 2% of our water is lost, with losses above 15% being fatal in most cases.

Water is essential for agriculture.  Indeed some of the earliest evidence of farming is represented by the appearance of irrigation ditches in Sumeria and Babylon. Today, crop irrigation leads to a build-up of salts, destroying the soil, while drought and flood are equally disastrous.

Deforestation has the potential to greatly disrupt water supply to the plains of Brazil.  Water evaporating from tree leaves in the Amazon forest forms the main source of water for rainfall on the Brazil Plains.  Removal of the forest means that water is not evaporated, and instead flows out to sea, threatening the Cerrado with extreme drought. 

Civil war, increasing population, deforestation, increasing agricultural pressures and climate destabilization all play a role.  In Tanzania the disappearance of the Kilimanjaro glacier will have a significant impact, as will reduced glacial melt for Peru. Many countries will fall below the acceptable minimum levels of water during the next decade.  We are draining aquifers of water at a rate higher than their rate of replenishment.

Already, the withdrawal of freshwater in quantities and at rates exceeding natural renewal capacities is documented in many parts of the world including China, India, Mexico, the Middle East, the Mediterranean region, Central Asia, Australia, southern Africa and the USA. The Aral Sea, formerly the fourth largest lake in the world has dried up, due to its feeder rivers being diverted for agriculture. Its disappearance has had wide-ranging impacts, from the collapse of fishing industry to regional climate destabilization.

Meanwhile glacial melt in the Himalayas threatens water flow in the Indus, Ganges, Brahmaputra, Irrawaddy, Mekong, Yangtze, and Yellow rivers, all of which have their sources in the Himalayan range. It is estimated that by 2100 AD, there will be a 30% decline in the Indus, the most important river in Pakistan. Agricultural losses are estimated at 8-24% in maize, soybean, wheat and rice by 2070 due to irrigation issues.

The groundwater footprint (GF) is the land area required to supply sufficient rainwater to underground aquifers in order to replace use of this water, divided by the area of the aquifer. The higher the value, the greater the area needed. Globally, 131 billion km2 is required to offset groundwater use, which is 3.5 times more area than is available.  Thus we are unsustainably using groundwater. This figure rises to >20 for High Plains (USA), North Arabian, Upper Ganges and Western Mexico aquifers, indicating that these areas are at high risk of draining aquifers completely, with devastating consequences. The Ogallala Aquifer (responsible for 30% of the irrigation water used by the US) is being emptied at record rates, with an average drawdown of 4 m across the eight states it underlies, and water levels have dropped by over 40m in some areas.

Our obsession with carbon has led us to ignore almost completely the cost of our lifestyles in terms of water. We are consumed with the carbon footprint of our foods, but ignore the water footprints. Water footprints of common  produce (including irrigation and processing) are huge:

Beef                                      1kg                                         15400 litres/kg

Pork                                      1kg                                         6000 litres/kg

Apple                                    1                                            125 litres per apple

Apple Juice                            1 litre                                     1140 litres water per litre

Banana                                 1                                            160 litres per banana

Orange                                 1                                            80 litres per orange

Pizza margherita                    1                                           1260 litres per pizza

Pasta                                   1kg                                         1850 litres /kg

Olives                                  1kg                                         3020 litres /kg

Egg                                     1                                            200 litres per egg

Cotton tee-shirt                    1                                            2500 litres per tee-shirt

Pair of jeans                        1                                            2500 litres per pair

Chocolate bar                      100g                                       1700 litres per 100g

Cheese                               1kg                                         5060 litres/kg

Wine                                  1 bottle                                   650 litres per bottle

Beer                                   0.5 l                                    148 litres per 0.5 litre beer

So to save water, drink beer not wine (or better still, drink water!), eat pork not beef, peel an orange, not a banana and stay clear of a plate of pasta, feta cheese and olives!

A final sector in which water consumption is often ignored is the energy sector.  Focus has been solely on the carbon footprint of energy production, rather than the associated water footprint.  The second table, below, shows the water requirements for a range of energy production methods.  As can clearly be seen, green fuels such as ethanol use large amounts of water compared with other fuels.  Given the already threatened water supplies, this could pose a significant threat to water security and demands re-evaluation in terms of sustainability.  Hydraulic power has a different issue: methane production.  When large dams are built the flooded vegetation releases large amounts of methane, a powerful greenhouse gas.

Process                                                                                      litres H2O/MWh

Geothermal                                                                                20

Petroleum extraction                                                                   40

Oil refining                                                                                 80-150

Oil shale surface retort                                                                680

Nuclear power plant, closed loop cooling                                       950

Nuclear power plant, open loop cooling                                         94,600-227,100

Corn ethanol                                                                              2,270,000-8,670,000

Soybean biodiesel                                                                      13,900,000-27,900,000

A fundamental point that I have stressed in my most recent book, Sustainable Economics: Context, Challenges and Opportunities for the 21st-Century Practitioner, is that there are three horsemen of the modern apocalypse, not just one.  We will fail if we focus only on carbon.  By the time we solve the carbon problem (likely when fossil fuels run out), the other problems will have already destroyed us.  For any hope, we must stop the reductionist thinking that has led us to the predicament that we are in, and, instead, embrace systems thinking. In other words seek sub-optimal solutions that work across all of the problems, rather than optimizing solutions to a single issue while ignoring the continuing chaos surrounding us. Ignore the manatee in the room at your cost.