The objectives of the research were to explore the use of concentrated sunlight combined with dissolved photocatalysts to improve water quality. Initial experiments with bromacil using organic-dye photosensitizers indicated that the reaction kinetics were enhanced by concentrated light. Other pesticides (EPTC, Tribufos, Atrazine and Lindane) were also tested in normal and concentrated sunlight. Organic dyes were effective in degrading some of these compounds but did not appear to be promising for complete mineralization. For most target compounds, the reaction rates were approximately proportional to the intensity of light. Iron compounds, especially in combination with hydrogen peroxide as the oxidizer, proved to be effective for degrading all the target pesticides. This system was also shown to mineralize phenol. Reaction rates were again approximately proportional to sunlight intensity. The photoefficiency of this reaction was in a range high enough to indicate that visible light, as well as UV, was participating in the photo-reactions. Preliminary disinfection tests have indicated that either organic dyes or iron compounds are effective. It is concluded from this work that solar irradiation with either organic dyes or the iron-peroxide system are a promising, possibly low cost, means of improving water quality.