An Environmental Decision Support System (EDSS) can be used as an important tool for rehabilitation and preservation of ecosystems. Nonetheless, high assimilation costs (both money and time) are one of the main reasons that these tools are not widely adapted in practice. This work presents a low-cost paradigm of "EDSS as a Service", this paradigm is demonstrated for developing Water Quality EDSS as a Service that utilizes the well-known CE-QUAL-W2 model as a kernel for deriving optimized decisions. The paradigm is leveraging new open-source technologies in software development (e.g. Docker, Kubernetes, and Helm) with cloud computing in order to significantly reduce assimilation costs of the EDSS for organizations and researchers working on rehabilitation and preservation of water bodies.