The concept of an "open" system architecture is an extremely attractive idea whose general practicability has been growing for the last several years. Standards are evolving, and continuing advances in hardware and software development support systems architectures that come ever closer to the ideal. The ideal is to have a set of information technology standards with supporting products that would make it possible for any conforming module, hardware or software, to interconnect and inter-operate with any other conforming module, or set of conforming modules, with little or no special effort. This paper examines the state-of-the-art in computer control systems from the perspective of open systems products as applied in the water and wastewater systems market. The concept of open systems is reviewed, and its significance and practical advantages are discussed. A survey of control system vendors who compete in the water/wastewater market was conducted, exploring available products and trends with regards to open system developments. The results of this survey are presented, which gives an overview of the extent to which open systems concepts have been incorporated into available products.