Abstract: The main objective of the current research is to evaluate the disinfection process of water supply system in highly populated area in the Gaza Strip based on world health organization limitations for residual chlorine to ensure the microbiological safety of drinking water. The study relied mainly on the measurements of residual chlorine in the drinking water network of Jabalia city in the period between February 2009 until April 2010 of fixed sampling points representing the whole area network. Digital colorimeter is used to measure free chlorine and/or total chlorine residual at the monitoring points. A DPD-1 (free chlorine) or DPD-3 (total chlorine) tablet is added to a vial of sample water that causes a color change to pink. The vial is inserted into a meter that reads the intensity of the color change by emitting a wavelength of light and automatically determining and displaying the color intensity (the free or total chlorine residual) digitally. The study showed that some concentrations of residual chlorine in municipal water distribution network was infringement of the allowed values according to WHO standards by 41.4%, moreover a high rate of residual chlorine in some monitoring points up than value of the chlorine injected into the source for Jabalia. The study confirmed the existence of inverse correlation between the amount of residual chlorine and the distance from the source of chlorination in water supply networks. The results were discusses and appropriate recommendations were done in order to maintain the quality and safety of drinking water.