Most pools experience between 3mm - 7mm of water loss each day, depending on where you live.
The average pool water evaporation rate is about a quarter of an inch of water per day or more than two inches in a week, which on a 33′ x 18′ swimming pool (an average pool size) is more than 2500 liters or approximately 600 gallons a week; this may vary depending on your climate and the factors listed above.
For example, high temperatures, lots of humidity, and high winds can increase your pool's evaporation rate. Pools without enclosures or tree cover will also evaporate faster than those with shade and protection because they are more exposed to the weather elements.
Losing a half-inch or more overnight indicates a problem. A covered pool or spa tub will lose very little water from evaporation in a 24-hour period. Check the water level in your pool or spa tub before you cover it and turn off the pump system. You will know if the water level drops below normal.
You can do the “bucket test” on your pool to measure evaporation. Place a bucket of water beside the pool and mark both the water in the bucket and the pool water level. Wait 24 hours then check the loss of both. If the pool loses more water than the bucket, then you have a leak.
This will vary depending upon several factors including: weather, if the pool is covered or not, bather load, and if it is heated or not. With pools that are covered, a good rule of thumb is that they should not have to be refilled more often than once every 2 weeks.
Look closely at the filter, pump, heater, and pipe valves, which is where leaks often tend to occur. If you have a vinyl pool liner, look for tears or separations around the fittings, lights, steps, and corners.
How Quickly Does It Evaporate? For evaporation, anywhere between 2 millimeters to 2 inches per week is about what you should expect in terms of pool water loss.
Pool Is Losing 1 Inch of Water Per Day
Losing more than ½” of pool water per day indicates you likely have a leak in your pool's structure or your pool pump system. You should call your pool service for a thorough leak inspection. You might not be able to keep up with refilling your pool at this point.
Re: Evaporation of Chlorinated versus Non Chlorinated water
Correct me if I'm wrong - but, you hypothesized that chlorinated water would evaporate faster, but your data showed that non-chlorinated water evaporated faster.
As a result, most evaporation actually occurs at night. This might seem counter-intuitive, but the reason is that at night the pool water is relatively warm, but the air temperature has dropped. What is this? Therefore, the difference between the air and water temperatures is greater – thus, more evaporation occurs.
Lower Your Water Temperature
As we know, warmer water evaporates at a faster rate than cooler water because the molecules are moving faster. As the temperatures drop, the warm water evaporates even faster.
Standing outside of the pool, inspect the pool's bottom all the way around. Most above ground pools are set on top of the earth, and when there is a leak in the vinyl, the leaked water travels through the earth and leaves noticeable valleys or divots where it was once flat.
RECOMMENDATIONS TO MINIMIZE WATER LOSS
The number-one way to combat evaporation is with a pool cover. It's estimated that a pool cover will reduce evaporation by 95 percent. Solar covers can heat your pool in the off-season, too. A pool cover reduces the pool's chemical consumption and reduces your cleaning time.
On average a water feature will lose ½% to 1% of the gallons pumped per hour in a day.
For an even easier and quick estimate, many people suggest using a linear loss rate of 0.25 inches of water per day during the summer. Using this rule of thumb, a typical 500 square foot pool may lose about 78 gallons of water per day.
As the temperature of your pool's water gets colder, the differential pressure between the water and the air increases. This speeds up the rate of evaporation. In addition, lack of humidity and wintertime dry air can also increase evaporation rates. The humid air during the summer keeps more water in your pool.
On average, swimming pools lose about a quarter of an inch of water each day, yet variations in wind intensity, humidity and sunlight can drastically change water loss rates. Some of the strongest and most intense wind in the country can be found in mountainous regions.
Pool Losing Water After Heavy Rain
Due to a heavy rainstorm, water loss is more common with vinyl liner pools that can be damaged, come loose, or float to the top. With other types of inground pools, it is vital to get the water level down. If not drained, the water balance will change, causing cloudy water and more.
A sinkhole can occur whether you have an inground pool or an above-ground pool. A pool that is allowed to leak into the foundation underneath can lead to a very large, very dangerous sinkhole. In fact, leaking water is the main cause of a sinkhole. Sinkholes start developing a long time before they actually appear.
Feel around the pool liner until you find a spot that's softer or squishes to the touch, which can indicate a leak. Put a few drops of coloring into the pool near the suspected spot. Coloring should mix with the water and let owners see how it flows. If it flows directly into the liner walls, you have found your leak.
Generally, pool water needs to be replaced once every five to seven years. This should be done during mild weather so that your pool surface is not at risk from strong sunlight and heat. Your pool maintenance company can recommend when it is time to drain your pool.
The surrounding environment dictates how long it takes for the chlorine to evaporate. Warmer air will cause the chlorine to evaporate more rapidly. If you decide to place the water in a jug that's left open in the refrigerator, the chlorine should evaporate completely within 24 hours.
An uncovered pool will lose water in the winter to evaporation in the same way it does during the summer. But the water loss is only about a quarter-inch on average during a 24-hour period when the pool is not in use. An uncovered or covered pool can have problems in the plumbing lines or pump.