In January, the World Economic Forum declared water the second biggest risk the world faces today - ahead of weapons of mass destruction and food shortages. For some businesses this did not come as a surprise, since they were already addressing the many issues around water management, scarcity and access that threaten their future prospects. From HSBC to Unilever, Coca-Cola to Diageo, major international companies are developing water projects as they recognise the value of investing in water.

However, on the twentieth anniversary of UN World Water Day, water remains a pipe dream for many. Nearly 800 million people around the world are still without access to clean water, and a further 2.5 billion people do not have adequate sanitation.

The issues around water are particularly pronounced on my continent of Africa. Women waste over 40 billion hours collecting water every year. In addition, children miss classes and girls all too often drop out of school when they reach puberty because of a lack of proper toilet facilities.

Interview: President Ellen Johnson Sirleaf

marks World Water Day

Water has the power to enhance life; it also has the power to destroy it. It is among the world's most prolific killers. Diarrhoea, from poor sanitation and dirty water, kills more children under the age of five than measles, HIV and malaria combined. At any given time, half of all hospital beds in developing countries are filled with people suffering from water-related diseases.

Poor health also translates into poor economic output. If children are not attending school, where will a country get its future doctors and engineers? If women and girls spend so much of their time collecting water, how does a nation develop its workforce?

It is estimated that a lack of safe water and adequate toilets costs Africa 5 percent of its GDP a year. To put this figure in perspective, it is equivalent to the amount of aid Africa receives from the donor community annually. Investing in water is therefore in everyone's interest.

Addressing the water and sanitation crisis should not be seen as charity, but as an opportunity. According to the World Health Organisation, every $1 invested in water infrastructure produces an average of $4 in increased productivity. You only need to look across Asia today, in South Korea, Malaysia and Singapore - all thriving economies and examples of results of investing in these basics services. In the last few decades, China and India have spent billions on water, helping the world reach its global target on water fives years ahead of schedule.

Next week President Susilo Bambang Yudhoyono of Indonesia and I will co-chair a meeting in Bali together with David Cameron's representative, Justine Greening. Our task is to lead the effort that will develop a bold, yet practical vision for international development when the Millennium Development Goals expire in 2015.

Because it touches on virtually every aspect of development, water and sanitation must be an essential part of this discussion. It will not be possible to make progress in eradicating poverty, reducing inequality and securing sustainable economic development without improving access to these services.

WaterAid, the international NGO, has stated that the new framework should include a commitment from world leaders to ensure that everyone, everywhere, has access to water, hygiene and sanitation by 2030. It will not be easy to achieve, but with political commitment, sound financial investment and innovative partnerships, we can get there.

While the support of our development partners is necessary to reach our goals, it is not sufficient. There is a Liberian proverb which says that if you want someone to wash your back, you must be prepared to wash your own front. Governments in Africa must show real leadership and live up to the ambitious commitments they have made. In collaboration with our donor partners, businesses and NGOs, we can get there. The historic milestone of water for everyone is within our grasp.

Ellen Johnson Sirleaf is the President of Liberia, winner of the Nobel Prize for Peace and Goodwill Ambassador for Water, Sanitation and Hygiene in Africa.