Normal Evaporation?

[Kit]

I have been monitoring the water level in my in-ground spa daily for the past 25 days with the auto fill off & the auto cover on (except as noted below). The reason? To rule out a possible leak. The results thus far are as follows:

Day 1 - 20: water level: -5/8" (air temperature = 85 - 90F).
Day 21 - 22: water level: -11/16" (cover off for 32 hours while SLAMming; air temperature = 93 - 97F.
Day 22 - 25: water level: -1/8" (air temperature = 96 - 99F).

Please note that the spa was used approximately every other day by my wife & I for about 1/2 hour during the 25-day period. There was no measurable splash-out ( even into the auto cover vault). The spa holds 2,500 gallons & has a surface area of 10' X 14".

:?:My question: Is it reasonable to assume that the decreases in water level noted above can be attributed solely to evaporation? Thank you kindly.

 

[Schadenfreude]

Seems reasonable. We have higher temps here (105-110 this time of year) and we probably lose a bit more than that with the cover on.

 

[pooldv]

Yes, 1/8-1/4 per day is normal evaporation without a cover. It could be about half that with a cover.

 

[mas985]

With a cover that covers 100% of the water surface, evaporation should be almost non-existent. Although I might classify 5/8" over 20 days as almost non-existent.

 

[Kit]

Thank you for the feedback. The thought also occurred to me that whenever the cover is retracted some water will be pulled into the cover vault. And speaking of incidental "spashout", is the amount of water that will cling to a person (assumingly wearing swimsuits) be of any significance as far as lowering the water level? (I have to admit that it seems like a silly question, but I have been surprised by the answer to stupider questions before). Nevertheless, I had to ask.

Thanks.

 

[gwegan]

First the best method to test for a leak vs evaporation is the bucket test. Place a bucket in a shallow area of your pool and fill it so the pool and bucket water levels are equal. If at the end of a few days they have different levels you most likely have a leak. I think you have evaporation but I would do the bucket test.

Even in a 2500 pool the amount of water on your clothing is negligible. usually less than a cup.

 

[Kit]

Bucket test! Brilliant! So simple & so obvious. The bucket is in the spa & I will report back in a few days. Thank you!!

 

[Kit]

Well, as promised, here are the results of the "bucket" test over the past 6 days. With the spa covered (except for about 1/2 hour of daily usage in the late evening), the water level in the spa fell 3/16". Air temperature: 87 - 100℉. Interestingly, the water level in the bucket fell 7/8" during the same period. I suspect that since the bucket was placed under a 1" opening in the auto cover, that might account for additional evaporation.

So, from your responses earlier, I assume that the decrease in the spa's water level was more than likely due to evaporation rather than a leak. Sound right?

Thank you for your help.