The article focuses on the process of water warming from 0 °C in a glass. An experiment is performed that analyzes the temperature in the top and bottom layers of water during warming. The experimental equipment is very simple and can be easily set up using devices available in schools. The temperature curves obtained from the experiment help us to understand the process of convection in the glass and to determine the temperature at which the density of water is maximum. In addition, computational fluid dynamics (CFD) modeling is carried out to facilitate better comprehension of the phenomenon observed in the experiment.