It is envisaged that future developments will allow refinements of the standard and particularly the development of practical guidelines. The method of water footprint accounting (Chapter 3) is now, after eight years of continued development, firmly established and widely adopted, both in the scientific community and in practice. The increased use of the water footprint in practical contexts in the past few years has contributed to maturing of the concept. Nevertheless, various challenges remain, including the development of practical guidelines per product category and business sector on how to truncate the analysis (where to stop going back along supply chains) and rules on how to account for uncertainties and how to deal with time variability when doing trend analysis. Besides, there is a huge challenge to develop databases on typical process water footprints (the basic ingredient for each analysis) and software tools to make it easier for practitioners to set up a water footprint account. Following the guidelines on water footprint accounting as provided in this manual is much more labour-intensive than when one could use a simple computer tool guiding the analysis. Developing such a tool together with underlying databases is therefore part of the work programme of the Water Footprint Network (WFN).