RICHARD LINDELL, REPORTER: Umushankar Sharma has plied his trade on the Yamuna all his life and the past two decades he's watched the river die.
UMUSHANKAR SHARMA, BOATMAN (translation): I feel very sad to see the river in this state. There was a time when the river was absolutely clean. There were tortoises, fish and other organisms living in the river, and today you can't find any trace of them.
RICHARD LINDELL: At one of the Yamuna's holiest places devotees make offering to the river while the poor bathe and wash their clothes. The water here is not from the Yamuna. The river's flow is halted by a levee built 100 metres north to protect the city's water supply.
CHANDRA BHUSHAN, CENTRE FOR SCIENCE AND ENVIRONMENT: What's flowing in Delhi is not water from the glaciers or water that the river's collected along its course upstream. But what's flowing in Delhi is raw sewerage.
RICHARD LINDELL: There are 22 drains like this one across the city pumping four gigalitres of sewerage into the river every day.
Here in the centre of Delhi the Yamuna River is clinically dead. In fact, what we're floating on here is little more than an open sewer. We can see methane bubbling to the surface, the smell of sulphur is quite unpleasant. And this is the water that tens of millions of people downstream are relying on.
Not just for household use, but also for agriculture.
SUNNY VERMA, ENVIRONMENTALIST, SWECHHA: We have looked at a study. Lot of research has happened on food quality when they use Yamuna water, especially on the banks of the river, and they have found large quantity of heavy metals in those food commodities. So the health impact is also very high.
RICHARD LINDELL: Delhi's residents use water piped from the Yamuna upstream. It's an inefficient and expensive system and the ageing infrastructure isn't up to the job. A third of the water is lost through leakage and only half the city has any plumbing at all.
In poor neighbourhoods people queue for hours behind trucks for water that is treated but still not safe for drinking.
CHANDRA BHUSHAN: There is a severe water crisis right now that the country is facing, Delhi is facing, especially during the summer months. It is really bad in Delhi. If you right now go looking for people fighting over water, you'll easily find people fighting over water next to water tanks within a radius of five kilometres from this place.
RICHARD LINDELL: Even connected neighbourhoods get just a few hours of water a day and pay for trucks to fill their tanks. Those that can afford it use filtered or bottled water for drinking and cooking.
Chronic shortages are not unique for Delhi. One third of Indians don't have access to a safe and reliable source of potable water.
SUNNY VERMA: Our infant mortality rate is probably one of the highest in the world still. Polluted water is the biggest baby killer in this country. We have problem of bacteriological contamination, on one hand, but also the issue of sporidiosis and arsenic. So unsafe water has huge health costs for this country.
RICHARD LINDELL: Delhi's government has spent hundreds of millions of dollars improving water quality, but the investment is a fraction of what's needed to cope with urban sprawl and population growth. Across the country rivers are choking and underground water tables are polluted and depleted.
Chandra Bhushan says climate change is making rainfall less predictable, but says there still should be enough water for everyone.
SUNNY VERMA: Delhi actually has low scarcity of water. The problem is distribution. In fact, there's a huge inequality in water distribution. Certain areas of Delhi get 500 litres of water. Certain areas don't even get 50 litres. So, one is inequality.
And secondly, it is about losses, losses in distribution system. In Delhi it's close to 30 per cent.
And the last point, which is the most important point in management, is the cost of water. People will have to understand economics of water. And unless and until we're able to charge true cost of water, especially from the rich, the system will continue. It's a combination of population, environmental impact, as well as management, that's leading to these problems.
RICHARD LINDELL: Climate change is expected to increase the volatility of India's monsoon, with up to 20 per cent more rain falling on fewer days. Scientists like Chandra Bhushan say massive investment is needed in rainwater harvesting, distribution and sewerage treatment or up to 1 billion Indians could face severe water shortages by the middle of the century.