Wastewater management receives a great deal of attention with various methods being proposed for discharge hazard estimation via ecotoxicological results. Policy-makers, stakeholders and the general public do not generally possess an adequate level of understanding on this matter, so it is rather hard to answer the question "How toxic is toxic?". The setting up and development of species-specific toxicity scores and a final wastewater toxicity index could avoid misinterpretations and confusion about toxicity data and different endpoints used and thus help wastewater classification and the management actions to be undertaken. Five-class toxicity scores were developed considering saltwater species. Toxicity scores outputs were then considered for a final index definition. This approach for wastewater assessment could be a suitable way to proceed in order to achieve environmental protection of water bodies, both fresh and saltwater, in accordance with the (near-)zero emission approach and the precautionary principle.