Second, to expand services to the poor without over-burdening already strained public budgets, policymakers should pursue innovative new partnerships with private sector actors. Of course, this requires effective regulation to protect consumers, together with strong governance structures to ensure that services can recover costs (and thus will be delivered consistently and at a high standard over the long term). For example, Kenya, in a bid to attract private investors, has provided shadow credit ratings of 43 utilities.

A significant opportunity exists for private actors to invest in providing affordable water-related services to poor and underserved segments of people in developing countries, owing to enormous untapped demand. In Bangladesh, Indonesia, Peru and Tanzania, the market for improved on-site sanitation services is estimated to be worth $2.6 billion.

Indeed, sanitation is the third area demanding greater attention. A vast percentage of the world's population lacks access to adequate facilities for disposal of human waste. Local programs aimed at changing communities' behavior could contribute to a cleaner environment and better health outcomes.

As the MDGs demonstrate, development objectives require a strong implementation framework, including sufficient financing and high-quality data, in order to scale up initiatives quickly while establishing accountability and ensuring sustainability. Here, national-level political leadership is critical.

Finally, world leaders must recognize that it will be impossible to address the water challenge effectively without confronting climate challenge. This demands a concerted effort to take advantage of opportunities for achieving sustainable growth, including by ensuring adequate investment.

Of course, there is also much to be done outside the water and sanitation sectors. In areas like agriculture, energy, forestry and municipal planning, decisions are taken daily without regard for their implications for water availability and sustainability - a situation that becomes even more complicated when water resources cross national boundaries.

In this context, more integrated, cooperative approaches are needed to improve water management.

But negotiations for water-cooperation agreements are fraught with perceived risks associated with issues related to accountability, sovereignty, equity and stability. Policymakers can mitigate these risks by building the institutions, knowledge and skills that are needed to manage water more effectively, including among households, farmers and businesses.

There is no single blueprint for international cooperation, but countries can learn from one another's experiences, employing strategies that have succeeded elsewhere to broker lasting agreements between competing interests. Such strategies must also be open to innovations in legal and financial instruments and guarantees, and they must be viewed as legitimate by diverse constituencies, including the youth who will inherit the arrangements that are created today.

Effective water management and sanitation have the power to transform economies - and the lives of the world's poorest people. There is no time - or water - to waste.

The author is the World Bank president's special envoy.

Project Syndicate