If you add more water vapor to a system at constant temperature, the total pressure will increase.
In a closed system, the pressure is determined by the number of gas molecules present and their average kinetic energy, which is related to temperature. When you introduce more water vapor into the system, you are adding additional gas molecules. These molecules will collide with the walls of the container more frequently, resulting in an increase in the total pressure.
According to Dalton's law of partial pressures, the total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases. Each gas in the mixture contributes to the total pressure based on its mole fraction and partial pressure. So when you add more water vapor, the partial pressure of the water vapor increases, and consequently, the total pressure of the system increases.
It's worth noting that the increase in pressure due to the addition of water vapor will be influenced by other factors such as the volume of the system and the presence of other gases. However, in general, adding more water vapor to a system at constant temperature will result in an increase in the total pressure.