The New Delhi Statement of 1990 called for universal water supply coverage by the year 2000, a goal that was later replaced by the Millennium Development Goals (MDGs) and the timeframe of 2015. As we are fast approaching this deadline, discussions are already under way for targets beyond the MDGs. In the wake of these developments, it is worth taking stock of what we can learn from existing efforts to measure access to water supply, sanitation and hygiene services. This article zooms in on one aspect of sector monitoring – national inventories – carried out in many developing countries as a first step to improve sector performance monitoring. Using the example of the National WASH Inventory in Ethiopia, under way in 2010/11, as a case study, we examine possible reasons why so often these costly and human resource‐intensive baselines tend to remain underutilised.