SONAULLAH PHAPHO has spent half a century picking a living from Wular lake high in Indian-controlled Kashmir. Today he is lucky if he scoops a fish or two out of the soupy mess. Push a boat into the knee-deep lake and the mud raises a stink of sewage. A century ago Wular and its surrounding marshes covered more than 217 square kilometres (84 square miles), making it one of Asia's larger freshwater lakes. Now, thanks to silt and encroachment, the extraction of water by nearby towns and tree planting on the shore, it measures only 87 sq km and is shrinking.

Compared with much of South Asia, Kashmir, a disputed territory in northern India, has many rivers and relatively few people. But even here fresh water is running short. To see how contentious this can be, drive half a day south to where the Baglihar dam (shown above) is rising up. An enormous wall bisects the valley, dressing it in white spray, and three huge jets of water blast from its sluices.

Half complete, the dam is already a local wonder that tourists gape at. It generates 450MW for the starved energy grid of Jammu and Kashmir. Once the scheme fully tames the water, by steering it through a tunnel blasted into the mountain, the grid will gain another 450MW.

The river swirls away, white-crested and silt-laden, racing to the nearby border with Pakistan. But there Baglihar is a source of bitterness. Pakistanis cite it as typical of an intensifying Indian threat to their existence, a conspiracy to divert, withhold or misuse precious water that is rightfully theirs. Officials in Islamabad and diplomats abroad are primed to grumble about it. Pakistan's most powerful man, the head of the armed forces, General Ashfaq Kayani, cites water to justify his “India-centric” military stance.

Others take it further. “Water is the latest battle cry for jihadis,” says B.G. Verghese, an Indian writer. “They shout that water must flow, or blood must flow.” Lashkar-e-Taiba, a Pakistani terror group, likes to threaten to blow up India's dams. Last year a Pakistani extremist, Abdur Rehman Makki, told a rally that if India were to “block Pakistan's waters, we will let loose a river of blood.”

Assorted hardliners cheer them on. A blood-curdling editorial in Nawa-i-Waqt, a Pakistani newspaper, warned in April that “Pakistan should convey to India that a war is possible on the issue of water and this time war will be a nuclear one.”

Upstream such outbursts are usually dismissed as proof that troubled Pakistan is, as ever, spoiling for a fight. Water is merely the latest excuse. India is not misbehaving, says Mr Verghese placidly. It fails to take all it is entitled to from cross-border rivers in Kashmir. Run-of-the-river dams like Baglihar consume nothing, since water must flow to run turbines. Such a dam, he says, merely briefly delays a river.

Indians point out, too, that Pakistan enjoys a rare guarantee: the Indus Water Treaty, struck in 1960 by far-sighted engineers and diplomats who saw that after the partition of land, water had to be shared out too. The treaty, which has survived three wars, details exactly how each side must use cross-border rivers. Mostly this applies to the tributaries that flow from Kashmir to form the massive Indus river, Pakistan's lifeblood.

If Indians abide by the treaty, then in theory at least they cannot be misbehaving. They see Baglihar as proof of co-operation, not a threat. When Pakistan objected to the dam's design, India accepted international arbitration, the first case in the treaty's history. Outside experts studied the dam and ordered small changes. But in effect they said it posed no threat to Pakistan. And last year the dispute was officially ended by the two governments.

Downstream, however, few sound satisfied. “The Baglihar decision…allowed a reservoir on a river coming into Pakistan, and now a precedent is set,” laments John Briscoe, a water expert formerly of the World Bank who advises Pakistan. The Pakistanis fear Indian control over the headwaters of the Indus. And Indian bureaucrats fuel these fears with obsessive secrecy about all water data.

Bashir Ahmad, a geologist in Srinagar, Kashmir who studied the Baglihar dam, gives grim warning about the Indians' future intentions: “They will switch the Indus off to make Pakistan solely dependent on India. It's going to be a water bomb.” A less excitable report in February by America's Senate offered a similar assessment: “The cumulative effect of [many dam] projects could give India the ability to store enough water to limit the supply to Pakistan at crucial moments in the growing season.” Dams are a source of “significant bilateral tension”, the report concludes.

More dams are to come, as India's need to power its economy means it is quietly spending billions on hydropower in Kashmir. The Senate report totted up 33 hydro projects in the border area. The state's chief minister, Omar Abdullah, says dams will add an extra 3,000MW to the grid in the next eight years alone. Some analysts in Srinagar talk of over 60 dam projects, large and small, now on the books.

Any of these could spark a new confrontation. The latest row is over the Kishanganga river (called the Neelum in Pakistan) as each country races to build a hydropower dam either side of Kashmir's line of control. India's dam will divert some of the river down a 22km (14-mile) mountain tunnel to turbines. To Pakistani fury, that will lessen the water flow to the downstream dam, so its capacity will fall short of a planned 960MW.

Pakistan also claims (though the evidence is shaky) that 600,000 people will suffer by getting less water for irrigation. Again it insisted on international arbitration at The Hague. In September, to Pakistani delight, India was ordered to suspend some of its building for further assessments to be made. But India still looks likelier to come away happy in the end, as the treaty foresaw and permitted the Indian design, and India is likely to finish its dam ahead of Pakistan in any case, by 2016 rather than 2018.

When China's upstream

Countries downstream have genuine reasons to fret. Pakistan is exposed. Like Egypt it exists around a single great river, though the Indus is nearly twice the Nile's size when it reaches the sea. It waters over 80% of Pakistan's 22m hectares (54m acres) of irrigated land, using canals built by the British. In turn that farming provides 21% of the country's GDP, as well as livelihoods for a big proportion of its 180m people. Many of them are already thirsty.

On average each Indian gets just 1,730 cubic metres of fresh water a year, less than a quarter of the global average of 8,209 cubic metres. Yet that looks bountiful compared with each Pakistani's share: a mere 1,000 cubic metres. Worse yet, South Asia's fresh water mostly falls in a few monsoon months. The dreadful floods this year and last showed that untamed and unpredictable rivers can be both resource and threat.

More rows between India and Pakistan are certain. India may keep on dismissing them as Pakistani bluster, an easy thing to do if you are upstream. But India is downstream in another highly tricky area: its border with China.

Tension already exists over the status of India's Arunachal Pradesh state, which China refuses to recognise. A quarrel over rivers in the region could serve as a focus for wider disputes about territory. A measure of the recent slump in relations came when, to the fury of India's authorities, China blocked an attempt by the Asian Development Bank to prepare for a dam project in Arunachal Pradesh. And one of India's largest rivers, the Brahmaputra (Tsangpo in China), flows south from the Tibetan plateau and into Assam not far from the disputed land.

Angry Indian politicians, activists, bloggers and journalists claim that water-starved China (with 8% of the world's fresh water but 20% of its population) has plans to divert the Tsangpo/Brahmaputra to farmers in its central and eastern regions. Feelings are running so high that India's prime minister, Manmohan Singh, felt obliged to issue a statement on August 4th saying that China's leaders had assured him there were no such plans afoot. And though a few run-of-the-river hydroelectric schemes are being built upstream on the Tsangpo, none of these could change the river's course. Cool heads point out that speculation about China channelling the torrent from near the border, at a spot known as the Great Bend, looks fantastical, at least at present. Chinese engineers would need to use nuclear explosions to have a chance of making tunnels through a series of ridged mountains to get water east from the Great Bend. Although plans have existed since the fourth century to take water from China's west to the east, and the scheme was pushed by Mao Zedong, the engineering, at least for now, appears to be technically impossible. Yet broader Indian strategic fears—the fact that the Chinese control the Tibetan plateau, which is the source of water for parts of densely populated northern India—will evaporate no more easily than Pakistani fears of India. An ever-thirstier region The scarcity of water in South Asia will become harder to manage as demand rises. South Asia's population of 1.5 billion is growing by 1.7% a year, says the World Bank, which means an extra 25m or so mouths to water and feed: imagine dropping North Korea's entire population on the region each year. Greater wealth in South Asia brings with it a soaring demand for food, especially for water-intensive meat and other protein. Industry and energy-producers also use water, though unlike farms they return it, eventually, to the rivers.

View the various territorial claims from

each country's perspective here

Worse, overall supply will not only fail to keep up with rising demand but is likely to fall (unless a cheap way is found to turn sea water fresh). The Himalayan glaciers are melting. A Dutch study last year of the western Himalayas reckoned that shrunken glaciers will cut the flow of the Indus by some 8% by mid-century. Flows may also get less regular, especially if glacial dams form, withholding water, and then collapse, causing floods.

Others give even scarier predictions. Sundeep Waslekar, who heads a Mumbai think-tank, the Strategic Foresight Group, which has picked water as a long-term threat to Asian stability, sees a “mega-arc of hydro insecurity” emerging from western China along the Himalayas to the Middle East and farther west. The strain of bigger populations, diminishing water tables and a changing climate could all conspire to produce a storm of troubles. South Asia is especially vulnerable: Mr Waslekar sees a cut of 20% in total available fresh water over the next two decades.

The greatest threat of all would be from any change to the monsoon, which delivers most of the region's fresh water each summer. Here, again, worries arise. Indian meteorologists who have studied rainfall data from 1901 to 2004 have noted signs in recent decades of more dry spells within the peak monsoon months. If these lead to weaker, or less predictable, monsoons in future (though this year's was about normal) the consequences for farmers could be dire.

When the water ran out In any case, the cost of running short of water is already becoming clearer. The Lancet, a British medical journal, reported last year that up to 77m Bangladeshis had been poisoned by arsenic—the largest mass-poisoning in history. It was the result of villagers pumping up groundwater from ever deeper aquifers. The same poison is now entering crops and more of the food chain. Filthy water and bad sanitation spread diseases, such as diarrhoea and cholera, which kill hundreds of thousands of Indian children every year, says Unicef, the UN's children's agency. Several South Asian rivers, suffering from weaker flows, have become a sludge of human and animal waste, dangerous to drink and wash in and unsafe even for watering crops. All over the region water tables are dropping as bore holes drive deeper. In the dry season even some of the larger rivers slow to a trickle. Knut Oberhagemann, a water expert in Dhaka, Bangladesh, says that the flow of the mighty Ganges where it enters Bangladesh is at times a pitiful few hundred cubic metres a second, so low that “you can walk across the river”. When the same river, at this point called the Padma, reaches the coast, it is often so feeble that the sea intrudes, poisoning the land with salt. The same problem curses the delta of the Indus in Pakistan. There a semi-desert was turned into some of the most fertile land on earth by British-built irrigation canals. But as the sea encroaches on low, flat land, rivers at times are flowing backwards, laments a local environmental activist. Take away the fresh water—around 60% of which is now lost to seepage and evaporation because of the bad management of those canals—and the desert will eventually come back.

Save or snatch

Governments in South Asia can respond to growing scarcity in one of two ways. The first is to improve the way they use the water they have, both by managing it better and by co-operating with one another. The second is to try to grab as much water as they can from their neighbours.

Better management of irrigation canals and better farming techniques would help hugely to cut waste. In Pakistan bitter rows between provinces have long scotched coherent planning. Wealthy Punjab, a big farming province, is routinely accused by downstream Sindh (and by others too) of taking an unfair share of the water.

And Pakistan badly needs more dams to control floods, store monsoon water and make electricity (China is said to have offered to help Pakistan build a series of big dams, and has already sent engineers to help speed along the new one on the Neelum/Kishanganga). Only about 10% of the potential hydropower of the Indus has been tapped so far, and only 30 days' average river flow can be stored (by contrast, the Colorado in America has dams to store 1,000 days'-worth).

Many governments are at least thinking in terms of dams and co-operation. Mr Waslekar reckons that 60-80 big dams (mostly for energy) will be built in South Asia in the next two or three decades, at a cost of hundreds of billions of dollars. In many cases—as for example in mountainous Bhutan, where the economy gets a huge boost from selling hydropower to India—this can foster economic and diplomatic co-operation. India has visions of one day persuading unstable but immensely water-rich Nepal to follow suit. The country is the source of more than 40% of the Ganges's water, and Indian analysts talk dreamily of 40GW of hydropower potential waiting to be used.

Other cross-border water deals are pending. Cosy ties with Bangladesh's government mean that India can more easily build dams on some of the several dozen rivers that cross their shared frontier. In September Mr Singh visited Dhaka to sign a deal with Bangladesh to allow the latest hydro dam to go up on the Teesta river. Though the deal was postponed at the last minute by a row with a regional Indian leader, it now looks set to go ahead. However there are bitter memories in Bangladesh of an earlier deal, on the Ganges, which allowed India to put up a barrage to block the river's flow in the dry season.

Tentative signs of wider co-operation exist. China issues twice-daily reports on the Tsangpo river flow in the flood season, separately to India and to Bangladesh. This could be seen as encouraging, if the two giants of the region wished to consider getting together over water. Indeed if full-scale friendliness were ever sought, an immense opportunity awaits.

Mr Verghese points out that the Tsangpo/Brahmaputra falls 2,450 metres (8,000 feet) over a few kilometres in China just before it reaches the Indian border. Send it through a 100km tunnel from the Tibetan plateau down to Assam and an enormous 54,000MW could be generated. One day its power could light not only much of north-east India and Bangladesh, but nearby Myanmar and beyond. Such a mega-structure would become a keystone for regional co-operation.

It will almost certainly never be built. Analysts have suggested that, given the generally dire relations between South Asian countries, water will provoke clashes rather than co-operation. A 2009 report for the CIA concluded that “the likelihood of conflict between India and Pakistan over shared river resources is expected to increase”, though it added that elsewhere in the region “the risk of armed interstate conflict is minor”. And a Bangladeshi security expert, Major-General Muniruzzaman, predicts that India's “coercive diplomacy”, its refusal to negotiate multilaterally on such issues as river-sharing, means that “if ever there were a localised conflict in South Asia, it will be over water.”