One of the main problems of the Whole Effluent Toxicity is related to the use of bioindicator species representative of the target environment. Most wastewater discharges are of fresh water, so their salinity has to be adjusted when they are discharged to transitional and marine coastal waters, in order to perform toxicity bioassays with reliable organisms. At the moment, there is no optimum technique to allow sample salinity to be adjusted and no specific information regarding salinity adjustment when bivalves are being considered for toxicity test performance. This paper provides information on the potential use of different methods to adjust the salinity of hotel/domestic wastewater samples with different brands of natural and synthetic Dry Salts (DS) and HyperSaline Brine (HSB) for use in the embryo larval development bioassay with the mussel Mytilus galloprovincialis. HyperSaline Brine derived from reconstructed artificial seawater proved to be more viable for wastewater salinity adjustment than DS.