Option 1: Boiling

Boiling is a common method of water purification that involves heating the water to a high temperature. This process effectively kills most microorganisms present in the water, making it safe to drink. Therefore, option 1 is not the correct answer because boiling does kill microorganisms.

Option 2: Filtration

Filtration is the process of passing water through a filter to remove impurities and particles. While filtration is effective in removing larger particles, such as dirt and debris, it may not necessarily kill microorganisms. Filtration alone might remove some microorganisms, but it does not guarantee complete elimination of all microorganisms. Hence, option 2 is the correct answer as it does not kill microorganisms.

Option 3: Chlorination

Chlorination is a method of water purification that involves adding chlorine to the water to kill microorganisms. Chlorine is a powerful disinfectant that can effectively eliminate bacteria, viruses, and other harmful microorganisms. Therefore, option 3 is not the correct answer because chlorination does kill microorganisms.

Option 4: UV-irradiation

UV-irradiation is a method of water purification that uses ultraviolet (UV) light to destroy the genetic material of microorganisms,