A highly produced man-made chemical primarily used as a solvent in the printing, rubber, and leather industries, and also widely used as a cleaning agent, paint thinner, and in varnishes. Xylenes can become water contaminants when they are discharged from petroleum and chemical factories when processing, transporting and disposing them. Although it is not usually found in high concentrations in drinking water, xylenes can have harmful effects on the liver, kidneys, lungs, heart, and nervous system.