This lecture covers the impact of water pollution, including the outbreak caused by Cryptosporidium parvum in Milwaukee, the introduction of tap water and water closets, and the effects of oxygen-demanding wastes on rivers. It also discusses eutrophication of lakes, measures taken in Switzerland, and the distribution of wastewater treatment plants. The presentation delves into the health effects of endocrine disruptors, the concept of decentralized water systems, and the organization of the course. Various topics such as dissolved oxygen levels, phosphorus models, and the development of phosphorus levels in Lake Sempach are explored.