Surface water contains biological constituents (primarily bacteria) that can contaminate the water-injection system. Because bacteria have the ability to multiply rapidly into colonies, they can:

• cause plugging of surface and downhole equipment and injection-well formations
• Promote corrosion of surface piping and downhole tubulars.
• generate H2S that can cause pitting corrosion

Therefore, it is essential to develop a means to control the growth of bacteria in surface-water-injection systems. Bacterial growth is controlled mainly by chemical biocides, which may be added directly or produced in-situ from seawater. Direct-added chemicals are covered in Water treating chemicals.