Scientists working closely on issues of water reuse are far from having solved all concerns related to the practice. From the very beginning of a water reuse project, scenarios must be prepared from the 'zero scenario' (no reuse) through to more complex and expensive ones (e.g. reverse osmosis for potable water treatment) to help stakeholders to select the best option for increasing available water resources, the ultimate purpose of reuse. In any case, the use of adequate tools to build scenarios is paramount. From Decision Support Systems to the simplest analytical tools, all knowledge is valuable. Detailed studies must be undertaken to identify necessary technologies, schemes and control tools. As public health concerns are normally among the main constraints for reuse any scenario will need to include detailed risk assessments. To achieve an adequate risk assessment, data pertaining to microbiological, chemical and biological factors is necessary. Unfortunately, suitable techniques and criteria are not always established by rules and regulations. However, several strong attempts have been made in some countries. Once the basic calculations were performed, a final decision whether the scheme can be implemented should be based on three phases of risk assessment; analysis, calculation and communication. This will allow fulfilling the key objectives of reuse: increasing the amount of water resources available, under an acceptable risk with a public full knowledge.