During the catastrophic 1984-5 drought in the Horn of Africa I was a member of a team of geologists at the UK’s Open University (Seife Berhe, myself, Paul Gibson, Dave Rothery, John Taylor and Matthew Willis ) who assessed groundwater potential in the affected area, using whatever remotely sensed data were available. That experience spurred me to write a book to help spread geological remote-sensing skills. In three editions (1987; 1993; 2001) Image Interpretation in Geology covered all aspects of the geoscientific opportunities presented by remotely sensed data and the means of acquiring them. Over three decades I ran courses and workshops for FAO, the USGS Mission in Saudi Arabia, various NGOs working in the Horn of Africa, the Department of Mines and the Water Resources Department in Eritrea and in 2004 and 2006 for the International Committee of the Red Cross, nearly all on water-related reconnaissance mapping. Image Interpretation in Geology (3rd edition) is now out of print. Rather than develop a fourth edition of the book I decided to focus on what I had taught and learned about groundwater exploration since 1984 through a free computer- and web-based practical course: this is the outcome.