The climate of Arizona, characterized by intense solar radiation, high daytime temperatures, and notably low humidity, presents a significant challenge for pool owners. Evaporation is consistently the largest single source of water loss for swimming pools across the state, far exceeding normal splash-out or minor leaks. Understanding the rate and causes of this water loss is the first step toward effective water conservation in this arid region.
Average Evaporation Rates in Arizona
The amount of water lost to the atmosphere from a pool in Arizona is substantial, especially when averaged over the entire year. The annual evaporation rate is approximately six feet of water, which is enough to evaporate the entire volume of a standard residential pool annually. This means that the average pool, which holds between 10,000 and 15,000 gallons, can lose nearly that much water over the course of a calendar year solely due to evaporation.
Daily rates fluctuate significantly depending on the season and specific weather conditions. This rate accelerates dramatically during the peak summer months of June through August. When temperatures are highest and humidity is lowest, pools can lose between one-quarter and one-half inch of water every day.
A standard 15-by-30-foot residential pool losing a half-inch of water daily translates to a loss of approximately 121 gallons per day. This higher rate means a typical uncovered pool can lose hundreds of gallons of water each week during the hottest parts of the year. This quantitative understanding of loss demonstrates why pool evaporation is a serious consideration for water management in the region.
Key Environmental Factors Accelerating Water Loss
High evaporation rates in Arizona are driven by environmental conditions that maximize water vaporization. Evaporation occurs when water molecules gain enough kinetic energy to break free from the liquid surface and enter the atmosphere as a gas. The desert climate amplifies all the primary factors that facilitate this molecular escape.
One of the most significant accelerators is the low relative humidity, which creates a large vapor pressure deficit between the pool surface and the surrounding air. The constant dryness of the Arizona atmosphere establishes a steep concentration gradient, ensuring the rapid and continuous transfer of water molecules into the air.
Wind speed also plays a substantial role by disrupting the boundary layer of air directly above the pool’s surface. This boundary layer becomes saturated with moisture from the pool, which naturally slows down further evaporation. This constant renewal of the air layer maximizes the rate of evaporation, even when the air temperature is not at its peak.
The intense solar radiation and high ambient temperatures increase the water’s temperature, directly boosting the kinetic energy of the water molecules. Warmer water means more molecules are moving fast enough to overcome the surface tension and escape into the air. This effect is compounded by the large temperature difference between the warm pool water and the cooler night air, which causes a visible mist of vapor to rise off the surface.
Effective Methods for Reducing Pool Evaporation
Pool owners have several strategies to mitigate the water loss caused by Arizona’s arid conditions. The most effective method involves placing a physical barrier between the water surface and the atmosphere. Solid pool covers, such as solar blankets, are highly effective, with some types reported to suppress evaporation by 85% to 95%. These covers not only trap water vapor but also reduce heat loss, which further slows the evaporation process.
A more convenient option is the use of automatic safety covers, which can be deployed with the push of a button and offer similar levels of evaporation reduction. For a less cumbersome approach, liquid pool covers apply a mono-molecular layer across the water surface. This invisible, ultra-thin film increases the resistance to water vapor escaping and can reduce evaporation by 30% to 50%.
Strategically placed landscaping or architectural features can also reduce the impact of wind, a major evaporative accelerator. Installing windbreaks like fences, hedges, or screens can reduce air movement across the water surface. By blocking the breeze, these structures help the humid boundary layer of air remain above the pool, which naturally slows the rate of water loss.
Finally, managing the pool’s temperature can offer a simple reduction in water loss. Evaporation rates are directly proportional to the water temperature, so simply lowering the thermostat, especially during overnight hours, reduces the kinetic energy of the water molecules. Pool features like waterfalls and fountains, which constantly circulate and expose water to the air, should also have their run times reduced, particularly during the hottest parts of the day.