Bacterial activities had an effect on petroleum industry through producing of H2S, within reservoirs or top facilities, which reduce oil quality, corrode steel material, and threatened workers' health due to its high toxicity. The main source of bacteria is water that injected inside the oil reservoirs.Most of the southern Iraqi oil field such as Rumaila, Zubair, and West Qurna are using hat Al-Arab water for injection to increase the reservoirs pressure and push oil towards production wells. The water of Shat Al-Arab contains a large amounts of bacteria and fungi. Therefore, during water treatment chlorine is added to the water in Qarmat Ali pump station to eliminate the bacteria, this process is costly especially with huge amounts of water. In this study a simple analysis of Shat Al-Arab water was conducted by applying gradual heat to the water sample simulating the increase of temperature with depth in oil wells, from monitoring temperature effect on bacteria, it was found that the Shatt al-Arab water bacteria can be killed at 70°C,and injection water may not require chlorine.