INDIA’S monsoon rains are retreating this week, a delayed end to a yearly wet season that has become ever more unpredictable as a result of global warming. Of all the challenges that face India, few are more pressing than how it manages water. In vast cities like New Delhi, where showers and flush toilets have become necessities for a rapidly expanding middle class, groundwater has been depleted. New Delhi once had many ponds and an open floodplain to absorb the monsoon and replenish aquifers; now the sprawling city has more concrete and asphalt than it has ponds and fields to absorb water.

India’s capital has come to rely for half its water on dams in the Himalaya range that capture monsoon runoff. But the dams disrupt the ecology of the Himalaya, South Asia’s precious watershed. Much of the waste from New Delhi’s overwhelmed sewage treatment system ends up in the Yamuna River, one of the main tributaries of the Ganges, which winds down from the Himalaya and flows 1,500 miles across India to the Bay of Bengal. Combined with under-regulated industrial effluents, urban waste has turned India’s mythic and misused rivers into cesspools.

In the countryside, where a vast majority of Indians still live, a combination of free electricity and inadequate regulation has led farmers to deplete untold groundwater supplies. In some places the water table is so low it no longer helps sustain roots, so even more water must be pumped up. In addition, soils have been degraded by chemical fertilizers, so they require even more water.

But in some parts of India, communities are turning to “rainwater harvesting,” capturing rainwater in ponds and allowing it to percolate into the ground to feed wells and springs. Such techniques were once commonplace throughout the South Asian subcontinent, where rain falls for only a few months in the summer monsoon, and often not at all for the rest of the year. Now villagers are returning to these ancient methods to secure the future.