Bacteria are simple, single-celled organisms. Many thousands of different species of bacteria are always around us. They have fundamental and essential roles to play in nature and are an integral part of our lives. The human body contains more bacteria cells than human cells. We are dependent on an important group of bacteria, those that help us digest our food. A few bacteria are pathogens, and some of these can be transmitted in water. In developed countries with drinking water disinfection standards and wastewater collection and treatment systems, deaths from waterborne bacterial diseases, such as typhoid and cholera, are uncommon. Nevertheless, in many parts of the world, these diseases persist because of the lack of water and wastewater infrastructure.