The level of water in the glass will typically decrease when the water is cooled from 40°C to 10°C. This phenomenon occurs because water exhibits a property known as thermal expansion, where it expands as its temperature increases and contracts as its temperature decreases.
In general, as water cools down, it becomes denser and occupies less volume. This means that a given mass of water at a lower temperature will occupy less space than the same mass of water at a higher temperature. Consequently, the level of water in the glass will decrease as it cools.
However, the exact change in water level will depend on various factors, including the specific properties of the glass and the water, as well as the exact volume of water and the shape of the glass. Therefore, without more information, it is difficult to determine the precise change in the water level in this scenario.