In this activity, learners investigate the different salinity levels of oceans, rivers and estuaries. Learners then use experimentation to determine which sample is the best model of each type of natural water source. The first test, for conductivity, shows learners that a water sample with the right salinity can even be used to light a bulb or ring an electric buzzer. The second test, for evaporation, shows how rate of evaporation is affected by salinity level. This activity can be followed by Water Body Salinities II from the same resource. Includes background material.