That 2.6 billion people live each day without a proper toilet is shocking. Break that number down, however, and it's even worse. Of these 2.6 billion people, the vast majority live in developing countries, this means that half the people in the developing world do not have a proper toilet. Take into account socio-economic status and the inequalities are worse still: in South Asia, amongst the poorest 40%, only 2 out of 10 households benefit from a safe, clean and dignified place to defecate.

Despite impressive development gains since 2000, we are simply not making much progress expanding proper toilet coverage. According to current trends, by 2015 - the year when global leaders will assess if we have reached the United Nations Millennium Development Goal target to halve the number of people lacking basic sanitation - more people, not fewer, will lack safe sanitation facilities. Daunting statistics, and behind them, immeasurable human suffering, a disheartening case of global inequity, lost opportunities for economic growth, and growing environmental degradation.

No one can ignore the costs that the lack of sanitation imposes at all levels. More children die of diarrhea, a preventable condition directly linked to fecal exposure, than of AIDS, malaria and measles combined. Even when diarrhea does not kill, it severely debilitates. It makes people, particularly the poorest children, more susceptible to acute respiratory infection and chronic under-nutrition and other afflictions. Fecal exposure also transmits tropical diseases such as trachoma, commonly known as river blindness, roundworm, hookworm, whipworm and schistosomiasis. If you are one of the millions upon millions of people suffering from these neglected tropical diseases, you just may be lucky enough to receive medication. But better sanitation could drastically decrease, and would eventually end, the occurrence of these easily preventable conditions for all, more cheaply than medication, while bringing a host of other development benefits.

Lack of proper toilets suppresses economic growth. The World Bank recently assessed the annual costs of poor sanitation in India at US$ 53.8 billion; $6.3 billion in Indonesia; and $193 million in Lao PDR - mainly due to health and environmental impacts. Imagine if all those dollars were spent on hygiene education, infrastructure projects and community development. We could end the sanitation crisis. Children, women and men would already be enjoying the health benefits, economic opportunities and basic human dignity that come with good sanitation.

You might ask yourself, why it is, in the year 2011, that 2.6 billion people don't have a proper toilet. Many capable people have tried to answer this question, and clearly there is not one single answer. Certainly, it is difficult to expand sanitation services in pace with rapid population growth. However, the experts all agree on a fundamental reason - decision makers are reluctant to speak publicly about sanitation and, as long as sanitation is stigmatized, the crisis will continue. We urgently need public education, targeted policy and, above all, the political will to tackle this challenge.

Today, I would argue, we are at a tipping point - more and more people are seeing sanitation's fundamental value and there are many reasons to be hopeful. Recently, the United Nations has demonstrated a genuine willingness to push sanitation to the center of the international development agenda. Countries have recognized that access to sanitation is a human right. And just a few months ago, UN member states passed a resolution calling for an end to open defecation, increased funding and coordinated action through the Sustainable Sanitation: Five-year Drive to 2015. This Drive to 2015, which will target decision makers in an effort to build political will for sanitation, will officially be launched on June 21 at the United Nations in New York. Please join our effort. In 2015, do we want more people to have a proper toilet? Of course, we do -- for 2.6 billion reasons!

• His Royal Highness, The Prince of Orange, is Chair of the United Nations Secretary-General's Advisory Board on Water and Sanitation.