Water injection is an essential part of many modem oilfield development plans. High-cost offshore developments require that the waterflood process equipment is designed and installed prior to acquiring any injection experience on that particular field. The chosen design must not only maximize the oil production revenue, but also carry an acceptable level of risk in terms of the project costs and technical uncertainties. This paper describes a holistic approach for an economic evaluation of the water injection process, integrating the key technical and economical elements. Well injectivity, which describes the well-to-reservoir connection, is a central factor in any water injection operation. The formation characteristics, water properties, well configuration and the injection water pressure determine this. Injection well behaviour is dominated by fracture geometry if the well is operated at sufficiently high pressure. By contrast, the injectivity of a well operated under matrix conditions (below fracture pressure) is dominated by formation damage caused by impurities in the injection water. This paper highlights the role of well injectivity provides a quantitative framework and a worked example of how decisions concerning design and operation of the waterflood plant, process and wells can be made.