1 Department of Zoology, Dr. Nazir Ahmad Institute of Biological Sciences, Government College University, Lahore, Pakistan.
2 Department of Earth Resources & Environmental Engineering, Hanyang University, 222-Wangsimni-Ro, Seongdong-Gu, Seoul, 04763, Republic of Korea.
3 Chemistry Department, College of Science, King Saud University, 11451, Riyadh, Saudi Arabia.
4 Department of Building, Civil and Environmental Engineering, Concordia University, Montreal, QC, H3G 1M8, Canada.
5 School of Environmental Engineering, University of Seoul, Seoul, 02504, Republic of Korea.
6 Department of Environmental Energy Engineering, Kyonggi University, 154-42 Gwanggyosan-Ro, Yeongtong-Gu, Suwon-Si, Gyeonggi-Do, 16227, Republic of Korea.
7 Department of Earth Resources & Environmental Engineering, Hanyang University, 222-Wangsimni-Ro, Seongdong-Gu, Seoul, 04763, Republic of Korea. bhjeon@hanyang.ac.kr.

Recent advancements in membrane technologies and disinfection methods have enhanced drinking water quality significantly. However, microorganisms, including free-living amoebae (FLA), persist and pose potential threats to humans. FLA are linked to severe neuro-ophthalmic infections and serve as hosts of pathogenic bacteria. This study examined FLA presence in chlorinated and ultrafiltration drinking water and evaluated chlorine's disinfectant. Of 115 water samples, 21 tested positive for Acanthamoeba sp., Allovahlkampfia sp., and Vermamoeba vermiformis, originating from chlorinated sources. FLA trophozoites withstand temperatures up to 37 °C, while the cysts tolerate heat shocks of 60-70 °C. Trophozoites are susceptible to 5 mg L^-1 chlorine, but cysts remain viable at concentrations up to 10 mg L^-1. FLAs' survival in chlorinated waters is attributed to high cyst tolerance and lower residual chlorine concentrations. These findings highlight the need for ultrafiltration or enhanced chlorination protocols to ensure safer drinking water.