Composition of Natural and Treated Water. Chemical and Microbiological Pollutants

Water is essential to sustain humans and human activities (e.g., food and energy production). Water resources are present to a large extent on the Earth's surface and in the subsurface. The possibility of using different water resources for human needs is not just a matter of water quantity, but more importantly a question of water quality (i.e., it is essential that the water has the correct composition to support different human uses). This chapter introduces the main physico-chemical properties of water and their relevance for global processes on Earth, and provides an overall description of the composition of water from a chemical and microbiological point of view with particular focus on chemical and microbial pollutants. As regards the chemical composition, the general properties of the main components potentially present in water are described, focusing on (i) the suspended matter in the aqueous phase, (ii) the gases dissolved in the water (with a focus on the natural role of oxygen and carbon dioxide), (iii) the inorganic compounds (and in particular on heavy metals as potential water pollutants) and (iv) the organic composition (distinguishing between natural organic substance and macro/micro organic pollutants). As for the microbiological composition of water, this chapter introduces some common aspects of water microbiology including (i) the main types of microorganisms in water, (ii) examples of microbial pathogens and role of biofilms, (iii) exposure routes for aquatic pathogens and the relationship between exposure concentration and risk of infection in relation to Quantitative Microbial Risk Assessment (QMRA), (iv) the concept of fecal indicators and water quality assessment, and (v) main principles and methods for water disinfection.