ABSTRACT
Until recently, intervention studies were rarely used to evaluate the level of endemic waterborne illness in populations. They were mostly used to monitor the effects of a new or improved water supply on the health of a population or to demonstrate the effectiveness of various sanitation procedures. In developing countries, intervention studies provided data on the reduction of various diseases in the population and the value of water treatment or availability to reduce waterborne diseases. However, results were often confounded by other factors linked to the overall sanitation and cultural habits of the populations studied. The true effect played by the water route is interlinked with these other factors, and any interpretation needs to be carefully validated. As water quality improves, it becomes more and more difficult to design and implement intervention studies that will not be subject to criticism and do not require a large number of followers.
