Can Water Under a Pool Cover Evaporate?

Evaporation

• Evaporation is the process by which water is transformed into water vapor. It converts the surface liquid of your pool into vapor that is then contained in the atmosphere. Evaporation is the cause of more than 80 percent of the earth's rain, snow or any form of precipitation. Several elements such as temperature, humidity and winds can also contribute to the current evaporation rate. Lower humidity and higher winds can accelerate the rate of evaporation.

Solar Covers

• Solar covers on swimming pools can significantly reduce evaporation. When evaporation is reduced it also increases the effectiveness of your pool chemicals. Solar covers are made of a thick, UV-grade plastic that creates a vapor barrier between your water and the air. This is how evaporation is eliminated. Pool professionals believe that more than 90 percent of evaporation can be eliminated by using a solar cover. Because an airtight seal is not created with the cover, evaporation can still occur, but not at a rate where it will be noticeable to the naked eye.

Benefits

• Evaporation rates can range based on several factors, but normal rates on average are somewhere between a one-half inch to no more than two inches per week. In some cases this number can be more. For those concerned about evaporation, leave the solar cover on as much as possible to control evaporation rates. These covers also heat the water.

Winter Covers

• Winter pool covers are installed in seasonal climates to protect you water against the harsh elements of the winter season. These covers are usually applied to the pool after the water level has been lowered and a flotation device is secured to the middle of the pool to redirect rain water to the outer edges of the cover. As a result, a large amount of air is present between the cover and the pool water. Evaporation is slower than without the cover, but will still occur over the course of several winter months.