If you talk about environmental issues, the way Bono and Chris Martin do,' says Corinne Bailey Rae, Yorkshire's nicest pop star and the latest celebrity to back a green charity, 'people think you're a self-righteous, arrogant nob.' She has a point. Make Bono History T-shirts are internet bestsellers, and Chris Martin is widely knocked as a fool. 'Like, even when Jamie Oliver made a TV show that affected government policy, people moaned that he was preaching. But isn't it amazing that a celebrity chef can have any impact on the world? In our country it's desperately fashionable to be hopeless. Being positive is seen as showing naivety. But I don't feel hopeless,' she says. 'I feel hope is really necessary for us to evolve.'

Bailey Rae is all about hope. And jazz. Hope, jazz and water. 'Because water is a feminist issue,' she says. 'Girls' education is seen as disposable, so they end up missing school, walking miles with unsafe water. It impacts hugely on women's lives, as well as the environment.' At 28 years old, she is the ambassador for Pump Aid, a charity founded in Africa that works with local communities to create sustainable supplies of clean water. They build pumps in rural Zimbabwe, Malawi and Mozambique, funded by the bottled-water brand Thirsty Planet. Every litre of Thirsty Planet sold generates 50,000 litres of water in Africa, and they aim to bring clean water to 10 million people by 2015: 50p from every multipack sold goes to Africa, where it will provide clean water for someone for life.

'I didn't realise just how amazing this organisation was until I went to Malawi in September,' Bailey Rae says. She talks fast and gently, scrunching her curls with her hand, articulate to the point of intimidating. 'We were brought up thinking of Africa as this dry, "cursed" continent, but there is water - you just have to go down deep enough to find it.' In Malawi she learned how to collect water using an ancient Chinese method - ropes are wound from grasses, attached to a rubber wheel and lowered 30 metres into the dry ground. 'A lot of other pumps in Africa have to be flown in, and parts have to be bought with cash,' she explains, 'but these communities don't use money, they just trade crops. Pump Aid's pumps only cost £250, while usually they cost about £2,000. I was amazed at the simplicity. And also humbled by the communities' gratitude. I mean, £250 really is nothing to us. Western people spend that on a handbag.'

The UK bottled-water industry is estimated to be worth around £2 billion. 'Yes, we have the irony over here that our water is absolutely fine to drink,' Bailey Rae starts, 'but we choose to buy bottled water. We think tap water isn't good enough for us.' Isn't this dodgy territory for the ambassador of a bottled-water charity? 'Thirsty Planet trades on that irony,' she says. 'The bottled-water industry isn't going to go away, but we're trying to get shoppers to pay attention to the fact that a billion people in the world don't have clean water. It's a way of jogging people's consciousness.' Also, she doesn't flush the toilet 'if it's just pee'.

'I was brought up getting a rainbow cardigan knitted in Guatemala for Christmas, or a doll made out of straw,' she explains. 'There were all these ways of trying to engage with Africa in a way that wasn't patronising. So, much as I love singing songs, I've always wanted to do more.'

Despite her passion for the planet, don't expect Bailey Rae's environmental concerns to surface in her second album. 'They haven't influenced my music yet, partly because I didn't feel like I could talk about the state of the world without sounding preachy. Besides, words like "multinational corporation" don't scan in a song.'

www.pumpaid.org; www.thirsty-planet.com