Cold water was poured into a bottle, into a flask in a canvas cover, and into a burnt earthenware jug.

Cold water was poured into a bottle, into a flask in a canvas cover, and into a burnt earthenware jug. Fired clay has a porous structure. In which vessel will the water be coldest after a while? The warmest?

The water stays cold for the longest time in the earthen jar. This is due to the porous structure of the fired clay, through which water seeps. This process cools the walls of the jug so that the water stays cold. That is why in Central Asia, where it is hot in summer and drinking water is worth its weight in gold, water is stored in clay jugs. The water in a flask placed in a canvas cover heats up relatively slowly, but the water in the bottle heats up the fastest.