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.
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. Some of the strongest and most intense wind in the country can be found in mountainous regions.
Depending on various environmental factors—including your location, average daily temperature, and the amount of sun your pool gets every day—your pool may lose more than half a centimeter of water every day. This translates to just under five centimeters a week, on average.
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.
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.
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.
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.
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. Not only can a swimming pool cover can keep more water in the pool, but it can also keep more heat inside the pool.
If you divide the distance by the elapsed time, the result will be the rate of water loss (evaporation). To convert this evaporation rate into gallons lost over a specific time period, you will need to convert the measure into a volume.
The cryogenic industry term Normal Evaporation Rate (or NER) describes the amount of cryogenic liquid that boils off to vapor during a given period of time.
The reason you don't want to completely drain your pool during winter is because the dry, freezing air can cause rips, cracks and tears in your liner. By allowing pool water to cover the liner, you're preventing the liner from drying up and getting damaged.
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.
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.
Daily as needed and indicated by measurement. One caveat, however: if your total alkalinity and pH are not where they should be, you will find it difficult to keep enough free chlorine in your pool water. Adjust your alkalinity first, then correct your chlorine.
Insulating the Pool Water from Heat Loss
Air bubbles in the pool cover act as an insulator in a similar way that your thermos would keep water warm. A pool cover will, therefore, keep your pool water warmer for longer.
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. Therefore, the difference between the air and water temperatures is greater – thus, more evaporation occurs.
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!
The pressurized plumbing system pumps water back to the pool after it has passed through the filter. The filtered water returns to the pool through the jet (or return) inlets. The plumbing that returns the water from the filter to the pool is often referred to as return plumbing.
Drain the water down to no more than 6 inches from the bottom of the skimmer if you plan to use a standard floating winter cover. Use your pool filter, switched to the "Drain" setting, to empty the pool water.
You don't need to drain your pool, as there is no risk to your pool by it being full. The only thing you lose with a pool filled to the rim is your skimmer's surface cleaning action. Overall, it still draws water and the equipment is just fine.
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.
Even with proper and regular pool maintenance, it's often necessary to drain your pool — completely or partially — every 3-5 years. Draining your pool often isn't necessary, especially if you're following a proper and regular maintenance program.