and sanitation for all by the end of 2025; to meet this target, some 2.9 billion people will need improved water supplies, and an almost unbelie- vable 4.2 billion people will need improved sani- tation.1 These figures translate into 310,000 people needing improved water supplies and 460,000 people needing improved sanitation per day during the 25 years to 2025. We should be able to meet the water target—we did better in the 1980s—but there is almost no chance that we will meet the sanitation target.4
So the world is not doing well in water supply and sanitation, and consequently not well in personal and domestic hygiene. However, our knowledge is great. Even so, there is a major problem: too few professionals in both tropical public health engineering and tropical public health medicine have (and even fewer apply) this knowledge. My eclectic historical review of relevant knowledge covers four major ‘milestones’ in our understanding of the relationship between water, sanitation and hygiene on the one hand, and health on the other. The first milestone is the following quotation from Hippocrates, who lived in the fifth and fourth centuries BC: “My other topic is water, and I now