Wastewater treatment systems help protect your health and the environment. Household wastewater from sinks, toilets, washing machines and showers— carrying dirt, soap, food, grease, bodily wastes and pathogens—flows down the drain and out of your house. Disease-causing microbes (pathogens), hazardous chemicals and nutrients such as phosphorus, nitrates and organic wastes found in wastewater can lead to human illness and polluted water. Wastewater must be treated before these contaminants reach groundwater—the source of well water—or nearby lakes, streams or wetlands.