Round and plane turbulent heated water jets discharged vertically into a stagnant uniform ambient water are considered. A differential turbulence model is used with numerical solution of the boundary layer equations. The International Equation of State for Seawater is used for the calculation of the buoyancy force. It is found that the buoyant jet characteristics are dependent on ambient water temperature due to nonlinear relationship between water density and temperature. This finding is of great practical importance for the design of thermal and wastewater diffusers. The design can be achieved efficiently using only mathematical models that include the water equation of state.