What condition must be met to ensure chlorine's effectiveness in water treatment?

Chlorine is a widely used disinfectant in water treatment, and its effectiveness is significantly influenced by the duration of contact time with water. Sufficient contact time allows chlorine to effectively kill or inactivate bacteria, viruses, and other pathogens present in the water. The longer the chlorine is in contact with the contaminants, the more effective it will be in achieving disinfection.

Factors such as water temperature, pH, and the presence of organic matter can also affect chlorine's efficacy, but the primary requirement remains adequate contact time. If the contact time is too short, chlorine may not fully act on all pathogens, leading to incomplete disinfection and potentially unsafe water.

While clear water can facilitate better disinfection by reducing interference from suspended particles, it is not a strict requirement for chlorine to be effective. Additionally, boiling water is not necessary for chlorine disinfection, and not all solids need to be removed for chlorine to work, although removing larger solids can improve overall treatment efficiency. Thus, ensuring sufficient contact time with chlorine emerges as the essential condition for effective water treatment.