Does Hot Tub Water Evaporate? How often you need to Fill it

Hot tubs are designed to heat water to extremely warm temperatures for your comfort and enjoyment. One of the few consequences of creating such warm water is that hot tubs are prone to evaporation. 

Hot tubs lose some of their water to evaporation because of the water’s heat combined with cool air. Hot tub water is more prone to evaporation in northern climates with cold winters, but evaporation can occur anywhere. 

No matter where you are in the world, your hot tub will lose some water to evaporation. How much it loses depends on the water temperature and the outdoor temperature. In this article, we’ll look at the factors that cause evaporation and the steps you can take to prevent it. 

How Much Water Evaporates? 

The amount of water evaporation that occurs in your hot tub depends on a number of factors. However, the average amount of water lost is around .5 to 1 inches per week. The temperature of the water, the outdoor temperature, and how often you use the tub will determine how much water is lost. 

Small group of female friends socialising and relaxing in the hot tub on a weekend away. They are celebrating with a glass of champagne.

It’s important to remember that not all water is lost because of evaporation. People often splash around and have a good time in hot tubs which also contributes to water loss. You also won’t lose much water to evaporation if you only use your tub once a week or every other week. The more you use it, the more evaporation will occur. 

What Causes Water to Evaporate? 

Without getting too scientific, evaporation occurs when water gets hot enough to partially turn gas molecules in the form of bubbles. Water doesn’t have to be boiling to evaporate, just warmer than the atmosphere. Evaporation is common during the winter months when the water is warm but the outdoor temperature is cold. The dryer and colder the air is, the more evaporation will occur. 

However, evaporation also occurs during the summer, simply because of how hot the water is in hot tubs. There will always be times throughout the day and night when the water is substantially warmer than the air and evaporation will occur. 

How Often Should I Add Water? 

There’s no real formula to determine how often you should add water to your hot tub or how much to add. You should check your owner’s manual and find out what the recommended water levels are. Once you have that information, simply add water whenever you need to in order to keep the hot tub full. You might have to add water once a week or once a month depending on how much you lose to evaporation and splashing around. 

Most hot tubs recommend the water level to be at least 1″ above the highest jet.

While you only need to add water as needed, it’s important to completely change your water from time to time. In fact, you should drain your hot tub and fill it with new water every three to four months, depending on how much you use it. Chlorine and chemicals go a long way towards cleaning your water, but a changeout is necessary periodically to provide clean, freshwater. 

Tips for Preventing Hot Tub Evaporation

While hot tubs will inevitably lose water to evaporation, there are measures you can take to reduce the amount you lose. Let’s look at some of the things you can do to save water and money in the process. 

Invest in an Air Tight Cover 

No matter what time of year it is, the best way to prevent evaporation is to invest in an air-tight hot tub cover. No matter how much you use your hot tub, there are more times when it’s sitting inactive than filled with people. 

Quality hot tub covers go a long way in preventing evaporation and saving you big bucks down the road. The more water you lose, the more you use and the more expensive your hot tub becomes. Most hot tubs come with a cover, but not all of them are high-quality and prevent evaporation. Investing in a specialty cover is an excellent idea, especially in cold areas. 

Utilize the Hot Tub Cover 

It goes without saying, but a hot tub cover isn’t going to do much good unless you actually use it. All to often, people hop out of the hot tub and forget to put the cover back on. It only takes a few hours to lose a decent amount of water to evaporation, so make sure to put the cover on as soon as you’re done. 

Use a Solar Blanket

A solar blanket will keep water and chemical evaporation to a minimum. This does add one step when you want to use the tub and one step when you want to be done, but trust me, it is worth it to save the life of your cover, reduce chemical use, and reduce water usage.

Use Cooler Water 

For some people, using cooler water defeats the purpose of a hot tub. Luckily, I’m not talking about drastic temperature reductions. Even lowering the temperature by one or two degrees can significantly reduce the amount of evaporation that occurs. It might not be worth it for everyone, but if you’re very concerned about water loss, cooler water is the way to go. 

Keep Your Tub in a Shaded Area 

Sunlight, heat, and wind can all increase the rate of evaporation with your hot tub. By installing your hot tub in a shaded area out of the way of the wind, you might just save yourself a few refills. 

Reduce Splashing and Jet Use 

Once again, less splashing and not using your jets goes against the grain of why you got your hot tub in the first place. However, jets and splashing will inevitably lead to more water loss and evaporation. As water moves around and bubbles, it becomes easier for molecules to get released into the air in the form of evaporation. Splashing also increases the odds of losing water over the sides of your hot tub. 

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