Which category of water is typically unsuitable for irrigation due to high contamination?

Black water is considered unsuitable for irrigation primarily due to its high levels of contamination. This classification of water typically includes wastewater from toilets, which contains pathogens, human waste, and potentially harmful substances. The presence of these contaminants poses a significant risk to human health and the environment, making it inappropriate for irrigation purposes. In contrast, gray water, which comes from sinks, showers, and washing machines, often has fewer contaminants and can be treated for reuse in irrigation. Rainwater is generally clean when collected properly, and surface water can vary in quality but is often used for irrigation with appropriate testing and treatment. Thus, black water is safely categorized as unsuitable for irrigation because of its high contamination levels, reinforcing the importance of understanding different water sources and their applications in facility management.