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.
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.
It is quite common for a pool to lose water over the winter. There are several reasons why a pool could lose hundreds of gallons of water gradually over the colder seasons. If the pool water continues to gradually decrease, the first and most common reason may be a small hole or tear in the pool liner.
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.
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.
How often should I have to fill my pool? 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.
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.
Evaporation rates are usually expressed as the water depth lost in millimetres over a period of time, e.g., 2 mm/day, 14 mm/week or 60 mm/month.
Most pools experience between 3mm - 7mm of water loss each day, depending on where you live.
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.
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.
On cold days, water evaporates, but it evaporates more slowly than it would on a warmer day. Although water can evaporate at low temperatures, the rate of evaporation increases as the temperature increases.
Although it may seem scary to leave water in a pool during freezing temperatures, you can actually damage your pool more by removing too much water. Your water should only be drained so it sits just below the skimmer and jets. This helps make sure that no water can get into the pumping system.
Cold weather generally results in low humidity. So, even though the vapour pressure of water is lower at cooler temperatures, the coincidentally low humidity allows a significant amount of the water to evaporate….
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.
If your pool lost water overnight and it is more than the quarter-inch due to evaporation, you probably have a leak. Evaporation accounts for a minor amount of water lost each day. Losing a half-inch or more overnight indicates a problem.
Use swimming pool covers to reduce evaporation!
They can dramatically slow down evaporation, particularly on hot days and cold nights. Studies confirm that covering a pool can reduce evaporation by up to 95%! That's big water savings! A swimming pool cover traps the vapors and the heat from escaping.
The differential that occurs between the pool water temperature and the air temperature on late summer nights causes water to evaporate at an accelerated rate. In some cases you might see a water level difference of 1-3 inches overnight. Depending on the size of your pool, that can be over 500 gallons of water loss!
Pool covers can be used on indoor and outdoor pools, as well as in-ground and above-ground pools, of almost any size or shape. Using a pool cover can prevent up to 95 percent of pool water evaporation.
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.
Evaporation occurs whenever you expose wind or air to the surface of your pool. So in short, this applies to every pool, all the time. Water molecules rise to the surface, form into a vapor and eventually get released into the air. Heated pools on cool nights experience evaporation more rapidly.
But did you know there's an easy way to reuse the water that's already in the pool? All you have to do is recycle it! Meet reverse osmosis — the best way to purify your swimming pool water. It works by pushing the existing water through semipermeable membranes that hold off any impurities, particles, and buildup.
The best way to keep your winter cover on your pool is simply to maintain 2 inches of water on top of it and keep it free of leaves and other debris and monitor the water level inside the pool regularly.
How long can you leave a pool empty? Well, the minimum amount of time possible in order to minimize the risk of serious damage. Most issues that require a pool drain will take at least a day or two to resolve, but it's recommended to not let it sit empty for any extended period of time.