Thirty-five Harvard colleagues and I are at the Kumbh Mela in Allahabad, India, a mass pilgrimage in which tens of millions of Hindus gather to bathe at the confluence of the sacred Ganga (Ganges) River, the Yamuna River, and the mythical underground Saraswathi.

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Another popular spot should be on the banks of the Yamuna river next to Agra's Taj Mahal.

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As for the Yamuna river, long the main source of the city's drinking water, it is clinically dead.

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Delhi draws three-quarters of its drinking water from the Yamuna river, into which the city dumps quantities of sewage, almost all of it untreated, to join a cocktail of farm chemicals and industrial effluents, including arsenic.

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Tens of millions of people - 30 million on the main bathing day on Sunday - bound by faith that a dip at the confluence of the Ganges and Yamuna river will get rid of their sins - throng the event.

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For 42 days starting on January 9th, the alignment of the stars makes Allahabad, where the Ganges, the Yamuna and a mythical third river converge, an especially holy place to be.

ECONOMIST: Take me to the river