THE trouble with water is that it is all politics, no economics. The costs of poor management are large: groundwater depletion takes 2.1% off Jordan's GDP; water pollution and scarcity knock 2.3% off China's; 11% of Kenya's was lost to flooding in 1997-98, and 16% to drought in the next two years. Rich countries build sewers, drains, dams, reservoirs, flood defences, irrigation canals and barrages to avoid such problems. Poor countries, with some exceptions, notably China, find large projects much more difficult. But at least large projects give politicians a monument to boast about. Small projects?weirs and wells and waterworks?have no allure for big-headed politicians.
That is a pity. A small dam is relatively cheap to construct: modest reservoirs known in India as tanks used to be built and maintained by local villagers. For a millennium they provided water in times of need and helped make rulers like the nizams of Hyderabad some of the richest men in the world. Now they are often silted up, polluted with pesticides, metals and phosphorus, or built on. In Kenya, by contrast, small dams are coming into fashion. Rainwater is channelled into sand catchments, which serve both to filter it and to protect it from evaporation. Some goes into nearby soil, for crops, some into groundwater from which it can later be recovered. In Niger a 15-year project involving dams and reclamation has restored nearly 20,000 hectares of unproductive land to forestry or agricultural use.
Everyone loves projects like these, especially if they can be given a romantic name like water harvesting. Some, perhaps, may simply be intercepting water for one user that would otherwise have gone to another, but almost every country could reduce its evaporation losses by capturing water and delivering it more effectively to the farmer, bather, drinker or manufacturer?and then, ideally, using it again. The harder question is whether that is enough.
Many believe it is not. Throughout history, man has made efforts to control water, divert it by means of canals, carry it via aqueducts, store it in reservoirs, harness it with water wheels and so on. The costs of these endeavours have been huge: valleys flooded, villages and habitats destroyed, wetlands drained and inland seas reduced to mere puddles. But the benefits have also been enormous.
The Aswan high dam, for example, is often cited as a cautionary example, a quixotic construction that now reduces the mighty Nile to a dribble before it trickles to the sea, leaving behind an explosion of water hyacinth, outbreaks of bilharzia, polluted irrigation channels and a build-up of sediment inland that would otherwise compensate for coastal erosion from Egypt to Lebanon. Yet, according to the World Bank, it has provided a bulwark against flooding for buildings and crops, a huge expansion of farming and Nile navigation (lots of tourism) and enough electricity for the whole of Egypt?all of which amounts to the equivalent each year of 2% of GDP in net benefits.
So would the World Bank today lend money for an Aswan dam if it did not already exist? The bank has been involved in few of the 200 or so large dams built in the past five years, but that is mainly because dam-builders?of which China is much the biggest?do not care for the bank's time- and money-consuming regulations, designed to ensure decent technical, social and environmental standards. Their strictness partly reflects greater knowledge about the consequences of building dams, partly the related political controversies of the 1980s. Even so, the bank was involved in 101 dam and hydro projects in 2007, up from 89 in 1997 and 76 in 2003; and it approved over $800m in hydro lending in 2008, up from $250m in 2002.
Suspicions of big dams still run high?and with some reason. Mr Thakkar, scrutineer of the Indian water scene, says that although the installed capacity of India's hydro projects increased at a compound rate of 4.4% a year between 1991 and 2005, the amount of energy generated actually fell. Some of the projects, poorly sited or poorly designed, were doomed to be uneconomic from the start. Others have been badly maintained or have simply silted up. But though 89% of the country's hydro projects operate below design capacity, the building continues wastefully apace.
Mr Thakkar argues that small projects offer much better returns, even for the crucial task of refilling aquifers by capturing monsoon rainfall. He points to the success of micro-irrigation in semi-arid Gujarat, whose agriculture has grown at an average of 9.6% a year since the turn of the century, partly thanks to the creation of 500,000 small ponds, dams and suchlike. But India, says Mr Thakkar, is still obsessed with big projects like the Bhakhra dam that the country's first prime minister, Jawaharlal Nehru, saw as one of the "temples" of Indian modernity. Only when the small temples can no longer provide solutions does he see a need for big ones.
Not all the big temples are dams. India has a dormant but not dead $120 billion scheme to bring "surplus" water from north to south by linking up the country's main rivers. China has its south-north equivalent, which, if it comes to pass, may involve spending $62 billion and shifting 250,000 people. Spain had its Ebro scheme, involving 830km of waterways, now abandoned, though some Spaniards remain wistful. Each of these has, or had, beguiling attractions, but vast costs.
Dams and reservoirs certainly need constant repairs and careful maintenance and do not always get them, usually because the necessary institutions are not in place. But when they are, a well-sited dam or embankment can transform lives for the better. In the late 1970s John Briscoe, an old water hand at the World Bank who is now at Harvard, spent a year in a Bangladeshi village and predicted terrible consequences if a proposed flood-control and irrigation scheme were to go ahead. It did, but on his return 22 years later he found the new embankment had vastly improved every aspect of the villagers' lives. He became an advocate of large projects.
In the rich world these are now largely unnecessary; the damage has been done and the benefits are being reaped. Southern California is an example, a region that gets all its water expensively from either the north of the state or the Colorado, a river so dammed and drained that it dies long before it reaches its delta?7,500 square kilometres of wetlands formerly crammed with wildlife, now invaded by the salty Pacific. But Hollywood survives, and in it such environmentalists as James Cameron, the director of "Avatar" and new champion of the Amazonian opponents of the planned Belo Monte dam in Brazil.
Many Ethiopians would be happy to have a few dams. Their GDP rises and falls in near synch with their rainfall, which varies wildly from year to year. If they had more storage, they could use it to get through the country's frequent droughts, but their man-made storage amounts to only 30 cubic metres per person, compared with 6,000 in the United States. Ethiopia's electricity consumption per person is among the lowest in the world, whereas its potential for hydro power is one of the highest. Indeed, electricity could be a valuable export.
Africa as a whole stands to benefit from more hydro projects, large and small. Climate change seems likely to shorten the rainy seasons and intensify variability, making storage even more important. Moreover, Africa seems likely to suffer more from climate change than other continents. As it is, it contains 35 of the 45 most "water-stressed" countries.
Hydro generation uses a known and tested technology that neither adds directly to greenhouse gases nor produces nuclear waste. Last month the World Bank announced a controversial $3.75 billion loan for a coal-fired plant in South Africa. Some hydro projects might be no more unpopular. Congo's Inga dams, for example, have the potential to provide the equivalent of South Africa's existing capacity. The South African authorities would be pleased to have it today. Their fingers are crossed that the hydro power from Mozambique will not cut out during the football World Cup next month.