Volatile organic compounds (VOCs) present in drinking water, have a negative impact on human health and environment especially that formed during chlorination step in the treatment process, they classified as possible human carcinogens, when exceed the permissible limits. The identification and quantification of VOCs performed by purge & trap GC/MS instrument, using reference analytical method (EPA 524.2, 1995). A monthly monitoring comparative study established during 2016 in both input and output of Shubra El-Kheima (Water Treatment Plants WTP) (1 km far from Nile River on Al-Sharqawia canal at the northern border of capital Cairo) and South Alamein WTP (270 km downstream far from the Nile River on Alhamam canal at North Coast of Egypt). The study investigated and recorded the presence of disinfection by-product of Volatile Organic Compounds (DBPs-VOCs) (CHCl₃, CHCl₂Br, CHClBr₂ and CHBr₃) which exceeded the permissible limits in the produced Water of South Alamein WTP and its boosters. The study succeeded in estimating the amount of granular activated carbon GAC required  to reduce (DBPs-VOCs) values from (178 µg/l) to (94 µg/l) in the produced water of South Alamein WTP, The duration frequency for changing (GAC)would be approximately (581 ton)/(17 days).