It is expected that carbon steel components in deaerated water such as in effluent water injection systems would have very low corrosion rates. The dissolved O2 content is such systems is typically below 40 ppb (parts per billion). However, slight ingress of O2 in the system through leaks in pumps, valves or gaskets can cause a dramatic increase in the corrosion rate of carbon steel which can be monitored with corrosion coupons and galvanic probes. It has been found that the corrosion morphology of such types of oxygen induced corrosion have quite unique characteristics. The present paper will provide some field results which will show the type of corrosion damage and morphology observed on coupons from an effluent water injection system. Data will also be presented to show how galvanic probes can be effectively used to detect and monitor oxygen ingress into the system during operation.