Water World
The world´s population is growing but the volume of fresh water is finite. How to keep everyone supplied with the planet´s most precious resource is a major challange.
One of the most popular misconceptions of the last 100 years is that the Great Wall of China can be seen from outer space – even from as far away as the moon.
Yet, despite evidence to the contrary from the American lunar landings and other space missions, the myth prevailed. It even featured in China’s elementary schoolbooks. But in 2003 the Chinese Ministry of Education decided to delete the reference after Yang Liwei, the first Chinese astronaut to orbit the earth, said he couldn’t spot the ancient structure during his 21-hour flight.
However what China couldn’t achieve with the Great Wall it certainly has with its colossal civil engineering project – the mighty Three Gorges Dam on the Yangtze River. Completed in 2009, it has been captured on fi lm by astronauts from the International Space Station via NASA’s Landsat satellites.
Twelve years in the construction, the dam was an undertaking of epic proportions. It is now the world’s largest, five times bigger than the mighty Hoover Dam in the US. The scale is staggering: 185 meters high and 2.3 kilometers across, creating a reservoir 660 kilometers long. That’s roughly half the length of California and one-and-a-half-times the size of Singapore. As well as providing much-needed drinking water to northern China the reservoir is also the world’s largest generator of hydroelectric power. Its 26 generators have the capacity to produce 18,200 MW, which is equivalent to the output of 15 nuclear power plants.
But the Three Gorges Dam has not been without controversy. It involved flooding thousands of villages and hundreds of towns and cities, displacing more than a million people in the process. Many archaeological sites are now underwater and there have been concerns about pollution. On the positive side, the dam controls the flow of the Yangtze so that the region is no longer at risk from the often catastrophic flooding that has plagued it throughout its history. Also the size of the reservoir enables large commercial ships to reach and therefore help boost the development of towns and cities up river.
Historically man has flooded valleys and submerged towns and villages to meet a growing thirst for water. In fact building dams is one of the oldest civil engineering skills. The earliest recorded dam was constructed across the Nile in Egypt, around 2900 BC. Amazingly there’s a dam in Syria, built in 1300 BC, which is still being used today.
Underground source
As we know, water is essential to all life on the planet and is the main reason why most civilizations have formed around rivers and lakes. Although water covers around 70 per cent of the earth’s surface, just three per cent of it is fresh water. And only about a third of that is available for drinking – the rest is frozen in the polar ice caps. Most of the potential drinking water is in underground aquifers, forcing humans to devise ingenious ways of extracting it.
Take qanats for example. Invented by the Persians, these were elaborate tunnel systems for accessing water in the dry mountain regions of what is now Iran. They ran for several kilometers and had vertical shafts at 20-30 meter intervals to provide ventilation and access for repairs. The main tunnel would run down to an outlet in the village from where the water would be distributed to the fields via canals.
Qanat technology spread throughout the Persian empire, including parts of Egypt and central Asian settlements along the silk route. The Romans also built qanats, as well as their famous aqueducts, for supplying water. Later, when the Arabs invaded North Africa and Spain, they took their qanat-building skills with them. Eventually, qanats appeared in Mexico, Peru and Chile, courtesy of the Spanish. Today qanats remain an important source of irrigation in Iran and many other Arab countries.
Another engineering achievement of ancient times was the water screw which was used for drainage and to transport large quantities of water from low to high ground. Its invention has been attributed to Archimedes and it’s claimed to have been used to water the Hanging Gardens of Babylon. But there is no real evidence to prove this. The Archimedes screw was simply a spiral structure inside a pipe. One end of the pipe would be inserted into the water then, as the screw was turned, it would scoop up water which would travel up the rotating spiral and out of the other end. Whether or not Archimedes was really behind this device, the idea has stood the test of time. Its design has formed the basis for many modern industrial pumps.
Although our ancient forbears left a legacy of water supply and sanitation know-how, it wasn’t until the last quarter of the 19th century that indoor plumbing became properly available. As knowledge of how water can be polluted or contaminated by disease-causing micro-organisms has increased, so have the ways of making it safe to drink. In the developed world a massive industry has grown around the collection, treatment and supply of water to homes, offices and other buildings.
In addition to underground aquifers, water for drinking is collected from springs and pumped from reservoirs. It is then purified and disinfected through chlorination. In some areas fluoride is added as a means of preventing tooth decay.
The waste water that is generated from sinks, baths and appliances can be treated and made potable. Water containing sewage and other waste is sent to waste water treatment plants.
Universal provider
Water’s ability to dissolve more substances than any other liquid has earned it the title of universal solvent. Yet, given the sheer number of ways we use and rely on water, it could be considered to be a universal provider. Water is the only natural substance to occur in solid, liquid and gas forms – and humans use all of them.
As well as drinking it, we grow crops with it, bathe and swim in it, wash our clothes in it and travel on it. Water is essential to many industrial processes as a chemical solvent, cleaner, coolant and hydroelectric power generator. Heat exchangers use both water and steam as a means of heat transfer and, under very high pressure, water makes an efficient precision-cutting tool.
Steam-driven turbines are used to generate electricity and steam also has effective sterilizing and cleaning properties. Anyone who has experienced a steam bath will probably tell you they feel much cleaner than if they had a standard bath or shower. In its solid form, ice, water enables us to chill and freeze foods so that they stay fresher for longer and can be transported for long distances.
Water can be ornamental – most major cities have fountains in their squares and parks. It’s also a provider of sports and recreation. These include swimming, waterskiing, surfing, skiing, ice skating,
snowboarding and ice hockey. In many cultures and religions water is seen as a purifier and numerous cleansing rituals have developed. New Year, in many south-east Asian countries, is celebrated by people pouring water on each other, a gesture of blessing and goodwill. Similarly, during wedding ceremonies in Thailand soaking the couple’s hands in water is thought to bring good luck.
It’s customary in parts of Japan to paint or carve the character for water on the roof of houses to protect them from fire – it’s believed that a roof with water on it will not burn. The Japanese use water for diverse rituals aimed at assuring a successful outcome for many of life’s key events, such as passing examinations, obtaining a new job or overcoming illness. During the winter Shinto devotees bathe in an icy pool at the Teppozu Shrine in Tokyo, supposedly to keep fit and demonstrate perseverance.
In fact, immersion in water is central to many faiths. Muslims and Hindus cleanse themselves before prayer and Christians are baptized in water that has been blessed.
Running dry
It’s an interesting fact that the volume of water on the planet is fixed. In other words, the water that existed when the earth was formed is the water we are using today. Nature recycles water constantly through evaporation and rainfall.
Theoretically, there should be enough fresh water to meet the needs of the global population several times over. But, in reality, it is unevenly distributed so that many parts of the world suffer from chronic shortages. The United Nations (UN) says that around 1.2 billion people live in areas where water is scarce and another 1.6 billion have limited access because their countries lack the infrastructure for obtaining supplies from rivers and aquifers.
But a combination of climate change, waste, pollution and increasing demand means that no continent will be immune from water scarcity. In its World Water Development Report, the UN predicts that, by 2050, one in four people will live in a country hit by recurring water shortages.
As countries become richer and more urbanized – most of the world’s population now lives in cities – their drain on water supplies increases. For example, in India water is pumped from tube wells at a rate of 100 cubic kilometers a year higher than the rains can replace.
Feeding a growing population adds to the problem. Agriculture already takes up around two thirds of fresh water use and that figure increases to 90 per cent in arid regions. It takes 5,000 liters of water to grow a kilogram of rice and nearly 4,000 liters to grow the wheat required to make a kilogram loaf of bread. Shortage of water has a devastating effect on the availability and price of food.
In 2008 severe drought in Australia resulted in a surge in food prices and, in 2010, Russia was forced to extend its grain export ban due to water shortages.
Taking action
So, how can we prevent the world’s fresh water supplies from running dry? The international community has woken up to the impending water crisis. One of the UN’s Millennium Development Goals was to halve the proportion of those without access to safe drinking water. To make this happen, the UN declared 2005-2015 the International Decade for Action ‘Water for Life’. It promotes actions and policies for better, more sustainable management of resources and improvements in sanitation.
Hot countries with limited rainfall are increasingly using desalination as a means of tapping into the vast water resources of the sea. However, a downside of this is that the desalination process requires expensive infrastructure and uses huge amounts of energy. Cogeneration, or a dual purpose facility, is one way of mitigating the effects. This is where excess heat from power generation is channeled into the desalination process. Most of these cogeneration facilities can be found in North Africa or the Middle East where fossil fuels for generating power are in ready supply. The prime example is the Jebel Ali power and desalination plant in Dubai. It’s the largest of its kind in the world and can produce 300 million cubic meters of fresh water per year.
Another innovation is to use wind turbines to power the desalination process. A Dutch company, called Dutch Rainmaker, is developing this technology. It is also applying the concept to extracting water from air. The wind turbine blades drive a refrigeration compressor and the evaporator within the system cools the air, causing it to condense.
But perhaps the most obvious, and cheapest, worldwide solutions to preventing water shortages in future are more prudent consumption, properly maintained infrastructure and better recycling.
Ensuring the supply of the world’s most important resource is in everyone’s interest.
More information:
- Waterwonders