He is used to taking on the daleks but now Dr Who actor David Tennant is tackling a real killer - contaminated water.The heartthrob has teamed up with fellow actors including Hugo Speer, Ian Kelsey and Claire Goose to film a new television advert to promote ethical water One - the brainchild of Norfolk entrepreneur Duncan Goose.

He is used to taking on the daleks but now Dr Who actor David Tennant is tackling a real killer - contaminated water.

The heartthrob has teamed up with fellow actors including Hugo Speer, Ian Kelsey and Claire Goose to film a new television advert to promote ethical water One - the brainchild of Norfolk entrepreneur Duncan Goose.

The advert, which has been shown on Channel 4 over the past three days, shows the actor talking candidly about the struggle one billion people face every day in getting access to clean water.

But thanks to Mr Goose, who grew up in Dersingham, near King's Lynn, and his celebrity promoters, the sale of One water is now directly funding water pump systems throughout Africa which provide clean water to those most desperately in need.

Today Mr Goose was at Covent Garden with sister Claire and Ian Kelsey to highlight the UN's World Water Day and ask people to think about what water they buy.

With an articulated lorry, given free for the day by Lynn Star Distribution & Logistics in King's Lynn, full of 30,000 bottles of One water Mr Goose was offering to trade empty branded water bottles for a full bottle of One and help launch a new campaign called Switch for Africa.

The campaign is in support of the United Nations Millennium Development Goal of halving water scarcity in Africa by 2015, and its target of providing indigent households with a minimum of 20 litres per person per day as a basic legislated right and free for those too poor to afford it.

He said: “If on one day everybody in the UK who normally buys bottled water - 26.5 million people - bought One water, that would pay for 374 pumps and help 935,000 people.”

Mr Goose, 38, puts all the money raised from selling his water into a not-for-profit organisation called PlayPumps International which is trying to bring clean water to 10 million people in Africa by 2010.

The PlayPump water system is a child's roundabout installed over sustainable boreholes. When children play on the roundabout it pumps water from depths of up to 100 metres and at a rate of up to 1400 litres per hour to a storage tank where it is then easily accessible from a tap.

Money raised by One has already provided clean water to around 75,000 people - that is 30 pumps serving an average of 2500 users each.

With the product now available at Co-op, Tesco, Morrisons and Waitrose stores, Total petrol stations, all UK university campuses and Heathrow, Gatwick, Stansted and Aberdeen airports it is hoped that it will sell 4.5 million bottles this year and fund one pump every 11 days by this summer, up to one a day in two years' time.

Claire Goose said that buying One water would directly help to bring clean drinking water to hundreds of thousands of African children for years to come.

“It's not just about the drinking water,” she said. “It's the wider implications which we in the UK take for granted. By having access to clean water, children can be children, they can go to school or play instead of walking hours every day to collect water. They can get an education and therefore have the best chance of rising out of poverty.”

Mr Goose said it was about making an educated purchase. “It is not about making money, it is the simplest way for people to do something that will actually benefit other people.”

Watch the advert online at www.we-are-one.org.uk.