The 6th World Water Forum was very intense and there is much to reflect on, but one memory stands out.
During the final two-hour session, Making Commitments and Mobilising Resources for Integrated Sanitation—Achieving Improvements at Scale , eighteen speakers had just five minutes each to summarize our collective insights on working at scale. Afterwards, Margaret Catley Carlson, former chair of the Global Water Partnership , expressed how happy she was with the summary. “At the last World Water Forum,” she said, “we could not have had such a discussion because the sector was too dispersed.” I agreed. In 2009, we knew the problems that contribute to 2.5 billion people without access to basic sanitation, but workable solutions to meet such a vast need were less certain.
Five years ago, the Bill & Melinda Gates Foundation approached the World Bank to discuss the challenges of working at scale to improve sanitation, especially in rural areas where access is strikingly low (according to WHO and UNICEF, an estimated 76% of urban dwellers use improved sanitation, compared to 45% of people in rural areas ). While there had been successful sanitation interventions, there was insufficient evidence that small pilots could be scaled up across an entire country. A partnership with the Water and Sanitation Program emerged out of these discussions. We developed a theory of change that challenged conventional thinking in several ways.
To increase access at scale, we reasoned, sanitation programs needed to be implemented at scale, working within existing national structures. In order to be sustained, sanitation programs needed to be led by national and local governments. And we believed that it was necessary to address both demand and supply, starting with behavior change in households and communities to increase demand, coupled with efforts to improve supply-- including products that that are affordable for all. Working in three countries, India, Indonesia, and Tanzania, we partnered with local and national governments and the local private sector to test, assess, and improve this theory. 
We’ve learned that it is possible to start at scale. Initially, we thought that these strategies could help governments improve sanitation for 4.45 million people in four years. As of July 2011, an estimated 10 million people have gained access.
And we’ve learned that national and local governments can take the lead. In the past year, new national rural sanitation programs based on this approach were announced in Indonesia and Tanzania. But there are also challenges and new questions such as, What is the role of government in scaling up what is essentially a private sector business?
Sanitation has many co-benefits, including health, economy, and the environment, and it was rightly highlighted in the 6th World Water Forum’s theme of Water and Green Growth. Rio+20  may be the obvious place to affirm that we are closer than before to reaching 2.5 billion people.