Munem Wasif Mall Galleries, London

The world’s first prize for photography concerned with the theme of sustainability, the Prix Pictet, was created in April 2008. Funded by the Swiss bank Pictet & Cie – and supported by the Financial Times – the prize’s inaugural edition focused on the subject of water.

The top award went to Canadian photographer Benoit Aquin, whose series on China’s dustbowl documented the world’s largest desertification process. But, as part of the prize, a shortlisted photographer was commissioned to record a water-related topic. Judges chose Bangladeshi photojournalist Munem Wasif, who competed with a black-and-white portfolio on climate change refugees in Bangladesh.

As part of his commission, Wasif set out to photograph a project managed by the charity Water Aid in the Chittagong Hills. When security in the area deteriorated, he had to find another subject. He directed his attention towards the residents of the Satkhira region in south-west Bangladesh, whose lives have been blighted by increased salinity in the water table.

Low-lying Bangladesh is particularly exposed to coastal erosion and rising sea-levels. In Satkhira, this exposure has been compounded by an increase in shrimp farming, which floods agricultural land with brackish water. In one of Wasif’s images, the interlopers writhe on a market floor like stranded aliens – whiskered and long-legged, seemingly semi-liquid in their translucent carapaces.

The consequences of salinisation are devastating. Once-fertile soil is rendered barren. Farmers are forced to eke out a living collecting the leaves of golpata palms in the Sundarbans swamps. Wasif catches golpata collectors trudging back with their payloads, the mobile mud beneath their feet ominously toothed with budding mangroves. A picture of golpata gatherers settling down for the night on riverboats has an eerie quality about it: the men and their boats are spectral.

One photograph looks like the monochrome record of an Andy Goldsworthy installation – an old wooden boat sitting on a neatly geometric platform of cracked mud. In fact, this is a patch of land that used to be productive, and has been desiccated by salt-water flooding.

Finding potable water is a never-ending job. As Wasif’s images reveal, women’s lives revolve around collecting it. They travel to the few sweet-water ponds twice a day, clay pots borne heavily on hips. The viewer’s eye is hooked by the metallic gleam of pitchers, watched over by women filling them up with water that trickles pitifully from wall-spouts.

Yet Wasif does not only illustrate the women’s travails. He reveals the school scantily attended because children must help their parents, or the child left sleeping alone while its mother seeks water. The most striking image – perfect in its composition, devastating in its implications – shows three brothers, knee-deep in mud, pushing boats loaded with fresh water containers. It takes them three hours to make that journey every day.

There are small mercies in this in-between world, caught amid the sea and the swamp. One villager has devised a system to gather rainwater and bags filled with it gleam as powerfully as the images of Shiva that decorate the hut’s interior.

Even the chairman of the Prix Pictet judges, Francis Hodgson, admits in the exhibition’s catalogue that viewers of Wasif’s pictures “will have at some point the sense of having seen them before”. What comes to mind most readily is the documentary work of the Brazilian photographer Sebastião Salgado – not only in the intimate and humane recording of human suffering, but also in the prints’ brooding low tones and the sharp highlights.

None of Wasif’s photographs are more Salgado-like than those of Amer Chan, suffering from a liver cancer exacerbated by high salinity levels. In its profound tenderness, the photo of Amer tended by his wife, Johura, is also reminiscent of Eugene Smith’s unforgettable images of mercury poisoning in Minamata.

Viewers may be caught in a dilemma common to documentary photography audiences: by what standards must we judge Wasif’s pictures? Are they damning evidence of environmental imbalance? Or are they arresting and aesthetically provocative images, fit to hang on a gallery wall? Wasif’s triumph lies in producing a body of work that falls into both categories.

  ‘Salt Water Tears: Lives Left Behind in Satkhira, Bangladesh’, to March 21, tel 020 7930 6844, www.prixpictet.com