It might be in 2004 or 2005 when I came to know about the Millennium Development Goals (MDGs), which was compiled following the adoption of the UN Millennium Declaration at the Millennium Summit of the UN in September 2000. Even though I had been mainly working on geophysical global hydrological cycles, quantification of world water resources and their relationship with  development, I was interested in the MDG Target 7C "Halve, by 2015, the proportion of people without sustainable access to safe drinking water and basic sanitation," one of 18 targets (later increased to 21) under 8 goals. At that time, I had never dreamed I would have the opportunity to work as a UN officer. The target seemed quite challenging and I thought it was merely a statement for international bureaucracies in the water sector to enhance their legitimacies and possibly to increase their budgetary situations.

However, I was stunned to see the 2012 WHO/UNICEF Joint Monitoring Report for Water Supply and Sanitation (JMP) which announced that Target 7C in terms of drinking water (Target 7C-Water) had been achieved in 2010, and I simply had to find out the reason why. I could not stop sending e-mails to my colleagues and acquaintances specializing in water and development at the Ministry of Foreign Affairs in Japan, Japan International Cooperation Agency, the World Bank, and the Asian Development Bank, - but nobody could give me a clear idea.

In April 2013, Ms. Shizuki Fukuda joined our research group as a 4^th year student of the International Project Course at The University of Tokyo’s Department of Civil Engineering. She was interested in the MDGs, and studied on the topic "How Achieving the Millennium Development Goals Increases Subjective Well-Being in Developing Nations" for her undergraduate thesis, which was published as a journal article on Sustainability (Fukuda et al., 2016).

In her graduate study, Shizuki continued her research on MDG Target 7C-Water through an extensive review of more than a few thousand pages of research articles and various reports by WHO, UNDP, and UN. The materials she looked into dated back to the 1950's, which included historical JMP reports. She had obtained such a large mass of information that it was difficult for Dr. Keigo Noda and myself, who were Shizuki's advisors on her master’s thesis, to understand what Shizuki could find out from these documents, and we suggested to Shizuki that she make a chronological table on what happened in the long history of global targets on drinking water. Honestly speaking, however, I could not fully understand what Shizuki had uncovered, and asked her to make a simple graphic illustrating the relationship between the GDP per capita and the proportion of the population who has access to improved water source. The message from the figure was clear, and it became Figure 2 of the present article, and I think her master’s thesis was satisfactorily convincing for the evaluation committee members. Shizuki graduated in March 2016 and started working in a consulting firm specialized in designing water supply systems.

We thought Shizuki's comprehensive review of the long history of global targets on drinking water was informative enough to be published as a journal paper, encouraged Shizuki to summarize the lengthy her master's thesis into a manuscript, and submitted it as a Review article in March 2018. It was, however, suggested that a Review article should present a review of researches on a specific topic, but not a review of a specific topic itself. Therefore we resubmitted it as an Analysis in November 2018 after substantial revisions. We are very pleased to see the final version of the Analysis since it was much more sophisticated than the initial version owing to the peer-review processes. Now we know it was not the first time for SDGs that 100 % coverage of access to drinking water is set, and we presume nobody, even among water experts in the world, has ever seen the chronological feature of the targets and achievements that the targets have been adjusted to keep the motivation (Supplementary Figure 6). It is a shame that we cannot say the MDG 7C-Water target was literally achieved since most populations in the world still cannot drink water from tap directly, however, it is a good news that increases of access to better water source is associated with economic development because we can concentrate on the efforts to enhance investments for developments or to improve the efficiency of investments through technological innovations.

We hope this research offers an insight into how we'll be able to achieve the Sustainable Development Goals, Goal 6 "Ensure availability and sustainable management of water and sanitation for all."

Taikan Oki

Special Advisor to President, Professor

Institute for Future Initiatives, The University of Tokyo

also Senior Vice-Rector, The United Nations University