the pores of the reservoir. Sand filters are a commonly used filtration technology. The sand filter has beds with various sizes of sand granules. The water flows through the first, coarsest, layer of sand down to the finest. To clean the filter the process is inverted. After the water is filtered it continues to the de-oxygenation tower. Sand filters are bulky, heavy, have some spill over of sand particles and require chemicals to enhance water quality. A more sophisticated approach is to use automatic self-cleaning backflushable screen filters (suction scanning). The importance of proper water treatment is crucial; especially with river-, and seawater, intake water quality can vary significantly (algae blooming in spring, storms and current stirring up sediments from the seafloor) which may have significant impact on the performance of the water treatment facilities. This may result in poor water quality, bioclogging of the reservoir and reduction of oil production. De-oxygenation Oxygen must be removed from the water because it promotes corrosion and growth of certain bacteria. Bacterial growth in the reservoir can produce hydrogen sulfide, a source of production problems, and may block the pores in the rock. A deoxygenation tower brings the injection water into contact with a gas stream (gas is readily available in the oilfield). The filtered water flows down the de-oxygenation tower, splashing onto a series of trays or packing causing dissolved air to be transferred to the gas stream. An alternative or supplementary method, also used as a backup to deoxygenation towers, is to add an oxygen scavenging agent such as sodium bisulfite and ammonium bisulphite. Another option is to use membrane contactors. Membrane contactors bring the water into contact with an inert gas stream, such as nitrogen, to strip out dissolved oxygen. Membrane contactors have the advantage of being lower weight and compact enabling smaller system designs. Water injection pumps The high pressure, high flow water injection pumps are placed near to the de-oxygenation tower and boosting pumps. They fill the base of the reservoir with the filtered water to push the oil towards the wells like a piston. The result of the injection is not quick, it needs time. Water injection plants The configuration of the plant elements described above and their operating conditions are outlined in this section. These examples are the former Amoco North West Hutton installation and the Buzzard installation in the North Sea. North West Hutton The