Southern California Evaporation

Debigold

Active member
Jul 1, 2018
28
San Juan Capistrano, CA
Good Morning Southern California pool owners,
Our weather here has been all over the place with days not consistant. Hot, Cold, Dry, Humid, Windy and Calm. I was wondering what your conditions and water evaporation has been?
Our pool is egg shaped, about 40 feet long and 16 feet at the widest point. There is a spa attached with overflow into the pool. We have 99% direct sun during the day. No trees, a very large yard for our area and since we are by the beach we almost always have a breeze or wind across our pool surface. We are losing an average of 1/4" a day. I tried to compare with our neighbor, but they have no clue due to they have an automatic water leveler.
I thought it was a bit much and thought we had a leak, but the pool service said it was normal for our area and surprised we are not losing more. He also said when we fill to proper levels the CYA would not be consistant. Since we have not had to add CYA there is not a leak. He tests cya once a month and a cya drop would be 1st indication of a leak. Im curious if he is correct or should I find another pool service?
 

Debigold

Active member
Jul 1, 2018
28
San Juan Capistrano, CA
Well thank you for that information. I dont know since you live in a different climate that the evaporation would be the same here. Your weather is much hotter than here, but I guess it all depends on the temp difference between water and air usually at night.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,811
Tucson, AZ
Well thank you for that information. I dont know since you live in a different climate that the evaporation would be the same here. Your weather is much hotter than here, but I guess it all depends on the temp difference between water and air usually at night.
While it is true that my hotter and dryer climate will produce greater evaporation, your question has been asked many times over the years and the general consensus from TFP users all over the USA is that a 1/4” to 1/2” of evaporation is pretty much the norm. Pan Evaporation data for Tucson collected from as early as the late 1890’s generally puts the July evaporation rate at about 12” to 13” which is about 0.4” per day. During the winter months when the temperature are substantially lower, evaporation is barely measurable.

You can loon through the California data at this website and see if any of the monitoring stations listed for California are near SJC. The tallies are broken down by months and the data is in inches of evaporation.


There are engineering equations that can estimate water loss based on air/water temps, relative humidity and wind speed if you know those parameters. Another method is to measure it yourself by doing a “bucket test”. If you search TFP for bucket test it will tell you how to do it. The bucket test is good for determining if you have a large leak, but it won’t pick up smaller leaks.

Both CYA and CH are very slow changing chemical levels. If either of those started to decrease suddenly, then you’d have a leak. As long as your not pump water out of your pool or rain isn’t overflowing it, those two chemical levels will be a good proxy for detecting a leak.
 
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bdavis466

TFP Expert
Platinum Supporter
Aug 4, 2014
4,963
San Clemente, CA
Im not far from you and your water loss sounds about right. Imagine if you left 1/4" deep puddle of water on the concrete - you think that would evaporate in a day?

If you're concerned with a leak then the bucket test is your best bet
 

Debigold

Active member
Jul 1, 2018
28
San Juan Capistrano, CA
While it is true that my hotter and dryer climate will produce greater evaporation, your question has been asked many times over the years and the general consensus from TFP users all over the USA is that a 1/4” to 1/2” of evaporation is pretty much the norm. Pan Evaporation data for Tucson collected from as early as the late 1890’s generally puts the July evaporation rate at about 12” to 13” which is about 0.4” per day. During the winter months when the temperature are substantially lower, evaporation is barely measurable.

You can loon through the California data at this website and see if any of the monitoring stations listed for California are near SJC. The tallies are broken down by months and the data is in inches of evaporation.


There are engineering equations that can estimate water loss based on air/water temps, relative humidity and wind speed if you know those parameters. Another method is to measure it yourself by doing a “bucket test”. If you search TFP for bucket test it will tell you how to do it. The bucket test is good for determining if you have a large leak, but it won’t pick up smaller leaks.

Both CYA and CH are very slow changing chemical levels. If either of those started to decrease suddenly, then you’d have a leak. As long as your not pump water out of your pool or rain isn’t overflowing it, those two chemical levels will be a good proxy for detecting a leak.
Thanks
 

Debigold

Active member
Jul 1, 2018
28
San Juan Capistrano, CA
I was only concerned due to the 7.1 magnitude earthquake on the 5th. It rocked us for about 50 seconds because we are so far from the epicenter. About 170 miles. Such a large rolling here in ViewPoint homes off of Camino Las Ramblas.(the very first houses here) We lost about 3 inches of water that splashed out of our 22,000g pool. 20 tiles popped off showing a crack in the upper portion of the beam and some on the decking.The beam is plaster the rest is a lot stronger pebbletec. The beam and tiles were not repaired or replaced when the pebbletec was installed. I worry about underground plumming since its about 45 years old. Did the bucket test which proved nothing as it zhowed more evap in the bucket than the pool. 🤣
 

LarsKev

Member
Dec 30, 2017
15
Los Angeles, CA
I live in Los Angeles (Westchester, near the beach), but my pool is in Cathedral City, and so it is a valid question to ask where one's pool is, since it may be at a different residence.
We were in Cathedral City during the earthquake, and it did splash quite a bit of water out of our pool, but I have no way of knowing how much water we lose. I do know we lose a lot every day from evaporation, but I was told that lawns use more water than pools.
ETA: I do notice now that my signature identifies where my pool is!
We're having our pool replastered in a couple of weeks but had no observable damage from the most recent quake.