There are many ways to prevent pool water evaporation, however, first you need to ensure the water is not leaking from your pool.
If you suspect there is a leak check your pool with the bucket test to find out if the pool is losing water quicker than evaporation. If so, you need to detect and fix the leak. Start with the filter as most leaks occur in the plumbing and filtration system rather than in the pool. If the filtration system is not leaking check the hydrostatic valve at the bottom of the pool as this is a common source of leaks.
Otherwise you are losing water due to excessive evaporation. There are many ways to prevent pool water evaporation to save water and money. Investing in a pool cover is the least expensive and most effective way to prevent pool water evaporation and keep your pool cleaner.
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What is Evaporation?
Evaporation is the process where liquid water changes to atmospheric water vapor. The molecules at the surface of the water must have sufficient kinetic energy to overcome the inter-molecular forces of the liquid. The kinetic energy of a molecule is directly proportional to its temperature so evaporation proceeds more quickly at higher temperatures.
Factors that Influence the Rate of Evaporation
The following factors influence the rate of evaporation of water from a swimming pool or any body of water.
1. Concentration of Water Vapor in the Atmosphere
The concentration of water vapor in the atmosphere is commonly called humidity.
When the atmosphere is dry the pool water will evaporate more quickly than when the air is already saturated with water vapor.
Water will evaporate quickly on a sunny, dry day and slowly on a wet or overcast day because on a wet day the air is already saturated with water vapor.
2. Surface Area
The larger the surface area compared to the volume of water the faster the rate of evaporation. There are more surface water molecules per unit of volume that can potentially escape the liquid into the air.
A wet towel will not dry very well if scrunched up. The towel will dry well if hung out flat on a clothes line where both sides are exposed to the air.
A large puddle of water, that is only 5mm deep and has the same surface area as a swimming pool, may dry up completely within a day. The swimming pool may take a year to dry out completely (assuming no rain) because it has a much larger volume of water.
3. Water Temperature
The higher the temperature of the pool water the faster the rate of the evaporation due to the increased kinetic energy of the molecules at its surface. Higher rates of evaporation occur when the water temperature is higher than the air temperature.
When water has reached boiling point all the water has enough energy to escape into the atmosphere. A pot of boiling water will completely evaporate in a short period of time.
Swimming pool water will evaporate faster in summer than in winter because it’s warmer.
Heated pool water evaporates faster than unheated water.
4. Air Temperature
The greater the difference between the air and water temperatures the higher the rate of evaporation. Water has a high latent heat capacity meaning it stores lots of energy and resists changing temperature. Water takes a lot longer than air to lose heat and fall in temperature.
More evaporation occurs at night because the air temperature falls quickly but the water temperature falls slowly and remains warmer for longer. So pool water evaporates faster at night when the air temperature is lower and the pool water is still warm.
During the day there is less difference between the air and water temperatures so evaporation will be less.
5. Atmospheric Pressure
Water will evaporate more quickly when the atmospheric pressure is lower because there is less exertion on the surface to keep water molecules in the liquid.
6. Rate of Air Flow
The higher the air flow over a swimming pool the faster the rate of evaporation.
Pool water will evaporate faster on a windy day.
How Much Water Does a Pool Lose to Evaporation?
The amount of pool water lost to evaporation depends on the above factors that influence evaporation. Generally, pools in hot and dry climates lose much more water than pools in cooler, wetter climates.
The average 8m x 4m swimming pool loses 2 to 8 litres per hour from evaporation. This will cause the average pool to lose a depth of 2mm to 20mm of pool water a week through evaporation.
During the warmest six months of the year your pool can lose up to 20% of the water due to evaporation. An average inground pool with 50,000 litres can lose up to 10,000 litres of water every year.
How to Prevent Pool Water Evaporation
The number one reason for losing water from your swimming pool is a evaporation.
Why do we want to prevent water evaporation from our swimming pools?
It’s not that we are all “greenies” trying to save the planet. But swimming pools consume a lot of water which has to be captured, treated, stored and pumped to your house. This takes a lot of energy and contributes to climate change.
If all pool owners have to top up the pool every week it’s costing you higher water charges. And the local water authority has to supply a lot more water to the city which means more dams, more water treatment facilities and more water storage tanks. Who pays for all that? You do as a tax payer!
So if you want to save the planet and pay less taxes implement some of the water saving measures below.
1. Cover the Pool
The first and most effective way to prevent pool water evaporation is to install a pool cover. A fully covered swimming pool will reduce evaporation by over 90%. The pool water is protected from the sun, wind and the atmospheric humidity. Most evaporation occurs at night so always cover the pool at night.
A pool cover will also keep your pool much cleaner as dirt and debris cannot enter the pool water. This will reduce the need to clean your filter as frequently and reduce the hours you need to run the pool pump. A cover will also protect your pool water from the sun to help prevent the evaporation of chlorine and other pool chemicals.
If you heat your pool water installing a cover when not in use will keep the heat in and reduce the cost of heating.
2. Solar Blanket
A solar blanket which floats on the pool surface is another way to prevent pool water evaporation. These solar blankets are a less expensive option than a proper pool cover but reduce evaporation and keep the water warm especially at night.
3. Glass Pool Fence
Installing a glass pool fence acts as a wind break to lower the rate of airflow across the surface of the water which reduces evaporation. The fence will also make swimming more comfortable as you will be sheltered from cool breezes.
A glass pool fence also helps to keep dirt and debris from blowing into your pool.
4. Wind Break
Installing a wind break like a wall, fence or trees will decrease the rate of airflow across the surface of the pool water which reduces evaporation. It will also give you more privacy from the neighbors.
5. Pool Enclosure
The ultimate protection from the weather and atmospheric conditions is a pool enclosure. Some pool enclosures are only insect screens which won’t prevent evaporation. However, a partial or fully glassed in enclosure will decrease the rate of airflow across the surface of the pool to reduce evaporation.
6. Turn off Water Features
Operating water features like fountains and waterfalls increases the surface area of water exposed to the atmosphere to increase evaporation. Turn off water features at night and when you are not at home to reduce evaporation.
7. Water Temperature
The higher the pool water temperature the more evaporation.
You can’t lower the water temperature of your pool in summer. But you should cover your pool especially during the summer season to prevent the increased loss of water from your pool. Covering the warm pool water prevents evaporation into the cooler night air.
How To Determine If Your Pool has a Leak
The number two reason for losing water from your swimming pool is a leak. The leak may be in the pool itself or more commonly in the filtration system and plumbing pipes. Watch this video to determine if you have a leak in your pool or filter.
The Bucket Method to Identify Leaks
- Select a fine, calm day with no forecast of rain. Wind and rain will void the test.
- Place a vertical strip of sticky paper tape on the inside and outside of a bucket. You are going to mark the strip of tape with a marker pen to indicate the water level.
- Fill the bucket to three quarters full with pool water. Don’t use tap water as it doesn’t contain the pool chemicals and salt, and will be at a different starting temperature which may cause a different rate of evaporation.
- Mark the water level on the tape inside the bucket.
- Place the bucket in the pool on the first step (or maybe the second step is better depending on your pool). You may need to place a brick or some heavy object in the bucket to keep the bucket on the step.
- Mark the waterline on the tape on the outside of the bucket with a marker pen
- Turn off the filtration system pump for 24 hours.
- On the next day compare the water level in the bucket to the pool water level. Normally, both water levels will have slightly dropped the same amount due to evaporation.
- If the level in the pool has dropped more than the level in the bucket then you probably have a pool leak.
- When you suspect there is a leak, repeat the test the next day but with the pump operating as normal.
- If the amount of water lost is the same as when the pump is off, the leak will probably be in the pool.
- Check the hydrostatic valve and skimmer box first as these are the most common places for a pool to leak.
- If the amount of water lost is more when the pump is on then the leak will probably be in the filtration system and plumbing.
Read our article on How to Find & Fix Swimming Pool Leaks
Conclusion
There are only two ways to lose water from your swimming pool – evaporation or a leak. The number one reason for losing water from your swimming pool is evaporation. However, you need to eliminate the possibility of the filtration system or pool shell leaking before trying to prevent pool water evaporation. I highly recommend purchasing a pool cover or at least a solar blanket to keep more water and heat in your pool while keeping out dirt and debris.
Please read our other posts and if you have any questions feel free to leave a comment below.
