For Victor Mallet the Ganges is a wondrous river of legend and history, but he is not a romantic. He is a hard-headed journalist who was chief of the Financial Times’ South Asia bureau for four years. He describes the legends and the theology that make the Ganges so sacred to Hindus, but at the same time he shocks us with the horrifying pollution of the river, and he provides nothing for our comfort, gives us little hope that it will become clean again.

The book starts at the source of the Ganges in the Himalayas, in terrain that Mallet describes as “starkly beautiful”. This beauty, he says, explains “why Hindus have long been in awe of the mountains that give birth to their holy river”. The source of the Ganges draws hundreds of thousands of pilgrims to perform their puja (worship) every year, but the most spectacular demonstration of Hindu devotion to the Ganges is the Kumbh Mela, held every 12 years at Allahabad, where the Ganges and the Yamuna meet.

Mallet attended the 2013 Kumbh Mela along with perhaps as many as 120 million others, like him intent on bathing in this particularly sacred place. He quotes Diana Eck, Harvard Professor of Comparative Religion and Indian Studies, as saying, “The river [Ganges] carries an immense cultural and religious significance for Hindus, no matter what part of the subcontinent they may call home, no matter what their sectarian leaning might be.”

At the 2013 Kumbh Mela there was no sign of the polluted waters of the Ganges deterring pilgrims from bathing. But in Varanasi, the most sacred city on the river, Mallet found the river “so visibly disgusting and malodorous in places that it discourages some of those who would otherwise take a ritual bath in the river”. Nevertheless, many do still bathe.

Mallet points out that the Ganges is not just sacred: it’s also vital to the lives of half the population of India, almost all Bangladeshis, and many Nepalis too. The dense population of the Ganges catchment area is one of the causes of the river’s pollution. Mallet quotes a World Bank official describing faecal contamination as “off the charts, ridiculously high”. The reason for this, according to Mallet, is that half of India’s 1.3 billion population has no access to a toilet.

The Ganges is also polluted by the effluent the industries situated in the towns and cities on its bank discharge, and the urban sewage spewed into the river. Mallet quotes a minister of the current government as admitting that nine-tenths of India’s sewage was still untreated.

The most alarming chapter in the book is ‘Superbug River’, in which Mallet discusses the growing global crisis of antibiotic-resistant diseases. Indian and American scientists agree that South Asia has been one epicentre of the crisis. Mallet quotes a research paper that reports high levels of an antibiotic-resistant gene associated with faecal bacteria in the Ganges during pilgrimage seasons.

Even if the gigantic task of solving the Ganges sanitation problem is completed, it will not be enough to keep the river clean unless the flow of water is maintained at a higher level. At present the flow is inadequate because of the water siphoned off for irrigation. Apparently only one-tenth of the Yamuna water that flows out of the Himalayas reaches Delhi. This, of course, has adverse consequences for the confluence with the Ganges and that river’s lower reaches.

It’s not as though there haven’t been attempts to clean the Ganges. In the 1980s the then prime minister Rajiv Gandhi launched an ambitious Ganges Plan, which failed. The best-informed and most outspoken critic of the Rajiv plan was Veer Bhadra Mishra, a professor of hydraulics and the mahant (head priest) of one of Varanasi’s most important temples. He died utterly disillusioned and silent because he felt all the time he had spent with journalists had been fruitless. Mallet was able to meet Veer Bhadra Mishra’s son, who is now the mahant. He is an electronics professor. The present prime minister, Narendra Modi, sought advice from him, but Modi has disappointed the mahant, describing his attempts to clean the Ganges as cosmetic.

Modi is the leader of a Hindu party and is the MP for Varanasi, and he sees the job of cleaning the Ganges as not just a political mission, but also a divine one. Speaking at a meeting to celebrate his election victory in 2014, he said: “Ma Ganga [‘Mother Ganges’] has decided some responsibilities for me… She is saying there must be one of my sons who will come and pull me out of this filth.” He too has his plan to rescue Mother Ganges, and aims to provide enough toilets to eradicate open defecation. But more than two years after that speech, Mallet found disillusioned citizens of Varanasi thinking it possible that Modi, like Rajiv Gandhi, would leave the Ganges “in a pitiable state”.

Modi’s plan for the Ganges is hampered by the inefficient and ineffective governments of the states in the Gangetic plain. Mallet describes them as “crippled by corruption, venal industrialists, the terrifying inertia of India’s bureaucracy”. But he does believe that fulfilling the task of cleaning the Ganges is possible. I fear it will prove impossible unless Modi or anyone else who might come to lead India energises the central government’s bureaucracy, curbs corruption, and prevents politicians from interfering with decisions that do not suit them.

The Harvard development economist Lant Prichett has said that India is not a failing state, but a flailing state. The flailing has to stop and the action has to start if the Ganges is to be cleaned. So far, for all Modi’s ability to convince Indian voters that he is a man of action, results have not shown that to be so. But Mallet gives us a glimmer of hope. He sees the administrative feat the government of one of India’s worst-run states, Uttar Pradesh, achieves in building the temporary city for the Kumbh Mela and managing the vast crowds at the festival as evidence that “good organization and efficient infrastructure … are no more impossible in India than anywhere else.”

Mark Tully is a former BBC India correspondent. He presents the BBC Radio 4 programme Something Understood.