The first two sections of this publication familiarize the reader with certain characteristics of solar radiation and its environmental and ecological impact, knowledge that is essential for photobiologists and photoecologists. We hope that it will provide valuable practical information and guidelines to benefit environmentalists and scientists engaged in the various aspects of photobiology in developing countries. The main emphasis, however, is on natural ultraviolet (UV) radiation, its role as a biocidal agent, and the monthly distribution of W-A intensity as it prevails throughout the year in Beirut, Lebanon.

The following sections are devoted to water disinfection and the development and assessment of a prototype facility with suitably designed "solar reactors" intended for experimentation on the photodecontamination of drinking water on a continuous-flow basis. In the event of its success after convincing field trials, this simple technology could then be transferred to developing countries, where solar energy prevails in abundance. Small rural communities, refugee and recreational camps, and institutions in remote areas would be some of the potential beneficiaries.

Much of the basic information and principles involved in the development of this system has been derived from previous research on the solar decontamination of water exposed to sunlight in transparent glass or plastic containers. The ultimate aim in this case was to provide water at the household level in rural communities deprived of safe drinking water. The study on the combined treatment of water with halogens and solar exposure, herein referred to as "halosol," forms another aspect of the research project supported by IDRC.

We hope that researchers elsewhere will endeavour to verify our findings and further develop the proposed water-disinfection systems to a practicable level for transfer to developing countries. Indeed, this would be a desirable contribution to the International Drinking Water Supply and Sanitation Decade.

A. A. American University of Beirut