The researchers studied how mixing raw water with treated wastewater can create harmful by-products when disinfected with chlorine. They looked at different sizes of organic matter in the water and found that smaller molecules were more likely to form these by-products. Coagulation with poly aluminum chloride helped remove some of the harmful substances, but larger molecules still contributed to the formation of certain by-products. To ensure safe drinking water, it is important to monitor the levels of treated wastewater mixed with raw water and improve water treatment processes.