New Delhi (CNN)Hundreds of empty plastic jugs wait in rows on the cracked, dry, dusty earth. Hovering expectantly nearby, the residents of Vasant Kunj slum in South Delhi, one of the city's largest and poorest, stand waiting for a government water tanker to arrive.
Water every 10 days: The families on the front line of India's environmental crisis
It's been 10 days.
Ten days since they last received a drop of water. For many families, their containers ran out days ago. They are thirsty and dirty.
"It's very difficult to live like this," said Fatima Bibi, 30, who is in charge of organizing water for the slum. "Everything comes from this water. Everything. Drinking, cooking, cleaning, washing."
Ten minutes away are Delhi's upscale shopping malls, where you can buy a pair of sneakers for $1,000. But in this part of the city, people live in tightly packed corrugated-iron huts. In the 40 C (104 F) heat, it feels like a furnace inside them.
As the tanker rolls into the compound, shouts rise up from the crowd. Men and women sprint forward with green rubber pipes to feed the tanker's water into their containers.
They are given 600 liters (158.5 gallons) per household -- barely enough to survive on until the next rations arrive.
India is facing the worst water crisis in its history, with 600 million people dealing with high to extreme water shortages, according to a recent report by Niti Aayog, a policy think tank for the Indian government. An average of 200,000 Indian lives are lost every year due to inadequate supply or contamination of water.
Twenty-one major Indian cities are estimated to run out of groundwater by 2020 -- just a year away. As India develops and grows to support its 1.3 billion people, those on the front lines of the crisis say it's only going to get worse.
"We have too many people for too little water," said Jyoti Sharma, founder and president of FORCE, an Indian NGO working on water conservation and sanitation. "It's unfortunate that people don't see how frightening it really is."
As arid countries like India get drier due to climate change, Sharma warned that water could soon become a global disparity issue.
Simply put, India's water sources are running out.
India's main problem is that the country relies on groundwater for most of its water needs. Decades of digging bore holes -- pipes that are drilled into the earth to reach water -- in favor of traditional water harvesting systems has meant India is suffering from severe ground water depletion.
"We are the largest groundwater user in the world," said Joydeep Gupta, South Asia editor at the Third Pole, a news website dedicated to environmental issues. "It's very bad, it's a state of very grave crisis."
As India becomes more urbanized and millions more people move to cities, there's an increased demand for water. Cities must look further and further afield for water sources, which are pumped hundreds of kilometers through pipes.
One hundred million people, including those in the large cities of Delhi, Bangalore and Hyderabad, will soon be living in zero groundwater cities, according to the report.
Added to this is that India is predominantly an agricultural country, with 80% of its water used to irrigate thirsty crops such as sugarcane and rice.
"Policies like several states giving free electricity to farmers or giving financial support for groundwater extraction -- borewells and tube wells -- results in uncontrolled exploitation and wastage of resource," Suresh Rohilla, director of urban water management at the Centre for Science and Environment told CNN last year.
Compounding the problem is changing climate patterns, which have made water supply far more uncertain. Monsoon rains have been more erratic and droughts more common, threatening farmer's harvests, Gupta said. Shorter winters and longer, hotter summers are increasing glacial melt in the Himalayas, which feeds into India's northern rivers.
It's a crisis that is playing out all over the country.
Depleting water tables, drought and mounting debt have caused a deepening agrarian crisis, and suicide among farmers has become a national issue. More than 200,000 have farmers killed themselves since 1995, according to government data collated by Mumbai-based NGO Down to Earth.
Last year, Shimla, in the northern Indian state of Himachal Pradesh, nearly ran out of water, spurring furious scenes of people scrambling for water, long queues and protests demanding water and urging tourists not to visit.
In major cities such as Bangalore and Hyderabad -- two big IT and tech hubs -- water tanker mafias are ruling who gets water and for what price as the cities are completely reliant on tanks for water. "There is a huge tanker mafia problem," said Gupta. "But it's the only way they get water."
Rural areas fare worse. When bore wells run dry, villagers are left without any source of water and are forced to walk miles or pay exorbitant prices for water to be delivered.
India's waterways have also turned toxic as billions of liters of wastewater -- including chemical run off and raw sewage -- is pumped into them every day.
"It's not unending. You cannot do this forever," Sharma said. "We are reaching the end game."
Water in India is now a precious commodity, and the people of Vasant Kunj slum are going to extraordinary lengths to conserve as much as possible.
Each household is allocated 600 liters (158.5 gallons) of free water by the New Delhi water board -- in summer and winter -- but residents say it's not enough to last the 10 days until the tanker delivers again.
Water dictates life here. Men and women out working are called back to the slum if a tanker is scheduled to arrive. There is no real set time for its arrival, though, and Fatima Bibi said recently the tanker came at 1 a.m.
"It's a whole day thing. They just have to wait to get the water," she said.
Her neighbor Ashraf Ullah is happy the tanker water has arrived. "It's cold water so the kids will love it," he said. "After 10 days in the plastic container, the water is boiling."
The lack of water is surprisingly a very visible presence in the slum.
Piles of black and blue water containers, each with separate markings for different families, are stacked up outside the huts, making the tiny lanes even narrower.
"We take half a bucket of water to bathe everyday, and some days we can't even have a wash," said Fatima Bibi. "Water is used to wash the vegetables. We'll then use it to wash clothes."
The water is used and reused and reused again. Even dirty water can be used again to clean elsewhere.
There are no taps or pipes. No drains. No sanitation. Buckets of slop sit outside every house -- not a scrap of water is wasted here.