How to handle evaporation?


LifeTime Supporter
Aug 18, 2007
Hello Everyone,

I recently learned that evaporation can happen at night as well from reading posts here. I thought I had another leak because the morning after the pump ran it seemed like the water level was low. I did a test yesterday where I brought the water up to a certain level, marked it and ran the pump during the day for the same amount of time that the pump runs overnight while I was home. the water level never changed the whole day.

The next morning, the water dropped some, so I'm guessing the overnight temps were cooler than the water which caused evaporation?

Anyway, my question is how do you all handle evaporation? are the pool levelers I see for sale online any good? or do I just monitor the level and add when necessary?

I want to make sure I don't get caught with the skimmer sucking air if I'm not home or come home later than usual.



Well-known member
Mar 29, 2007
Ontario, Canada
Your water level should be high enough on your skimmer that you shouldn't have to worry about it evaporating
below the skimmer... at least for more than 1-2 days. You do loose quite a bit overnight due to the colder air temps.
The number 1 way to slow down evaporation overnight is a solar cover. I put mine on every night and have only had to top up my pool maybe 4 times this summer. You also hold in a lot of your heat if you use a solar cover. You can also turn your
return jets down so that your pool stays calm which will help with evaporation. Other people have had success with the liquid solar fish blanket.


LifeTime Supporter
Aug 18, 2007
Yes, it would be about every 1-2 days where I'll have to refill. It's between 1/4 - 1/2 it seems to depend on the day. For example last night, seems to be less than 1/4.

A solar cover, I'll have to check that out...thanks!

Also, one of the pool guys cut off one of the returns that drips water on the top of the pool. Should I have him reactivate that, so that water is running on the surface and will help maintain the temperature in some way?



Well-known member
Jun 30, 2007
North Florida
The amount of evaporation can vary greatly depending on the time of year, where you live, surface area of your pool, and the siting of your pool, just to name a few factors. You can search and (hopefully) find the pan evaporation rates for your area.

Pan evaporation is a measure of the amount of evaporation that might be expected from a water body. While it's often used for lakes and reservoirs, it still has significance to your pool. Some sources indicate that one should use only 75% of the pan evap rate as an indicator of true evaporation due to the way pan evap is measured. For me, I don't need it to be that precise, just a general indication of how much my water level might decrease.

As an example, the average pan evaporation rates for my area of North Texas are 9.5 inches in May, 11.21 in June, 12.66 in July, 11.7 in August, and 8.78 in September. If you divide any of those rates by 4 or 5, you'll see about how much water I might lose to evaporation each week, assuming no added rainfall. (Even if you use just 75% of the readings, it's still quite a bit of water loss due to evaporation! :shock: )


LifeTime Supporter
Aug 18, 2007
I live in AZ so as you can imagine, it gets hot. It has cooled off the past couple of days so i've had no evaporation to speak of.

I'll check out some solar covers, thanks for that tip!


LifeTime Supporter
Jul 25, 2007
Alamo, CA
A simple test would be to fill a bucket with pool water and leave it next to the pool for a couple of days. It should go down about the same amount as the pool (unless the bucket's water gets much hotter than the pool in the sun).

Another thing that many people don't realize about evaporation is that it is the cause of most of the pool's heat loss. I read somewhere that at least 90% of the heat loss is due to evaporation, so preventing evaporation will extend your swimming season, too.


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
bluenoise said:
A simple test would be to fill a bucket with pool water and leave it next to the pool for a couple of days. It should go down about the same amount as the pool (unless the bucket's water gets much hotter than the pool in the sun).
The easy way to keep the water in the bucket the same temp as the pool water is to set the bucket on the pool steps for an inground pool, or ty it to the ladder on an AG.


TFP Expert
LifeTime Supporter
May 3, 2007
Pleasanton, CA
Just measured mine a few weeks ago and I was averaging 3/8" per day. It was a very hot week in the 90s and yes I have done a bucket test recently so no leaks.

My daily average according to this Link is about 3/16" which is half what I measured so worst case is about twice the daily average. I suspect winter time here is near zero evaporation so the average works out.