Perimeter Overflow and Evaporation

[goldmaes]

I am a new pool owner and new to this Forum, so please bear with me.

The new home I purchased has an incredible raised perimeter overflow pool with a further raised spa that spills on 3 sides into the pool and one side into a trough. We love everything about the pool however our water bills are out of control. I am estimating that I am using between 10k to 15k more gallons of water each month than I ever have in any month. I know it will be more as I live in South Florida however my water bill should never be more than my electric bill. The pool is approximately 680 sq ft.

As a result, I believe there may be a pressure side leak as the pool seems to lose water when the pump is on, however I cannot locate where the water would be going. That being said, the pool company is trying to convince me that it would be reasonable to expect that this type of pool would evaporate 3/4 of an inch of water per day or more!!!! This seems insane to me. I have tried to research but there doesn't seem to be. any good sites on what to expect with a perimeter overflow pool and they are all set up differently.

I was wondering what everyone's thoughts would be on this in this forum.

Please feel free to ask questions. Thanks

 

[Texas Splash]

Hello and welcome to the forum! Wonderful pool you have there, and it's unfortunate you suspect a leak. I too would be concerned about a 3/4 inch drop per day. Before you assume the worse though, you might consider looking at our Pool School - Leak Detection page. You'll find some tips there which may help you confirm (or hopefully deny) any leak. You mentioned more water loss when the pump is on. Does there appear to be any significant water loss when the system is off?

I would also recommend updating your signature with all of your pool and equipment info. It can help us later when trying o answer your questions. Keep us posted on this thread and I'm sure others will chime in to assist.

 

[JamesW]

What is the water temperature?

 

[goldmaes]

Right now the water is at about 71 degrees F.

 

[goldmaes]

Hello and welcome to the forum! Wonderful pool you have there, and it's unfortunate you suspect a leak. I too would be concerned about a 3/4 inch drop per day. Before you assume the worse though, you might consider looking at our Pool School - Leak Detection page. You'll find some tips there which may help you confirm (or hopefully deny) any leak. You mentioned more water loss when the pump is on. Does there appear to be any significant water loss when the system is off?

I would also recommend updating your signature with all of your pool and equipment info. It can help us later when trying o answer your questions. Keep us posted on this thread and I'm sure others will chime in to assist.

Thanks for your replay. No there doesn't seem to be any water loss when the pump is off. Unlike many others there is only one pump for the pool. The pump fills the pool over the edge and the water spilling the into trough is gravity fed back to the collection tank. The autofill is located inside the collection tank. I imagine with the problem only occurring with the pump on, I suspect a pressure side leak, but, there doesn't seem to be any other visible signs of a leak. Any thoughts would be greatly appreciated.

 

[kimkats]

Here is a link to a thread about the "bucket test" for water loss:

Bucket test accurate?

Let us know what you find with this.

 

[Texas Splash]

At this point, I also think a pic of your equipment and updating your signature is important. One thing to consider - do you have a sand or DE filter? One with a multiport valve (MPV)? If so, something bad in the MPV (i.e. spider gasket) could be compromised allowing water to flow to waste without you even knowing it. So the more we know and see about your equipment and set-up the better.

 

[duraleigh]

3/4 inch daily loss in Florida is a leak, not evaporation.

Do the bucket test to confirm. 1/4 daily is around max evaporation for Florida pools.

 

[goldmaes]

3/4 inch daily loss in Florida is a leak, not evaporation.

Do the bucket test to confirm. 1/4 daily is around max evaporation for Florida pools.

I agree with you that 1/4 seems more accurate. The reason I mention this is that they are trying to state that 1/4" is appropriate if the pool was not a perimeter overflow pool, but they are telling me that 3/4 is evaporation because the water flowing over the weir evaporates more quickly. Does anyone with a similar pool (knife edge, infinity, etc) agree???

 

[mas985]

Evaporation occurs at the water air boundary and with an overflow, you do increase the surface area of the evaporation. It is hard to tell from the picture but if the overflow area is the same size as the pool area, you will approximately double the evaporation rate from the pool alone. Also, it might actually be a little worse than that because the water going over the edge is turbulent which also increases the surface area of the water.

Also, if you turn off the pump, the water overflow is also turned off so the evaporation will go down to the same rate as the pool alone.

If you can give me an estimate of the pool area and the overflow "water area", I can estimate the amount of evaporation increase that is theoretically possible.

 

[AUSpool]

Ive been through this, my pool evaporates almost 4 times the local areas pan evaporation levels when the temp gets up. Mostly due to exposure to prevailing wind. The perimeter overflow would add to evaporation and an increase would coincide with when the pump is on. Do the bucket test.

Heres an evaporation calculator to play with; https://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

And my experience; https://www.troublefreepool.com/thr...e?highlight=Evaporation&p=1154774#post1154774

 

[PoolguyinCT]

Evaporation occurs at the water air boundary and with an overflow, you do increase the surface area of the evaporation. It is hard to tell from the picture but if the overflow area is the same size as the pool area, you will approximately double the evaporation rate from the pool alone. Also, it might actually be a little worse than that because the water going over the edge is turbulent which also increases the surface area of the water.

Also, if you turn off the pump, the water overflow is also turned off so the evaporation will go down to the same rate as the pool alone.

If you can give me an estimate of the pool area and the overflow "water area", I can estimate the amount of evaporation increase that is theoretically possible.

I’m looking forward to the estimate. Which tool are you using? ASLA has several for public use.

A Water in transit vessel, without calculating can easily approach 3/4” daily evaporation.

Bucket testing is tricky as 4 vessels are present.
Bucket test will also be invalid, without draining below pool spill walls.
Pool, spa, surge tank & perimeter collection slot.

High water bills don’t guarantee a pool leak.

Water in transit pool leaks are a quite different, always start with the surge tank and the valves which isolate the vessels listed above.

Hopefully it is a true leak or no leak and not a design flaw.

 

[mas985]

I’m looking forward to the estimate. Which tool are you using? ASLA has several for public use.

I have yet to find anything online that has all the features as the tool I developed. It does a full heat transfer calculation including heat gain components; sun, solar, gas heater, heat pump, solar cover and all the heat loss components; evaporation, radiation, convection, conduction. It is available to anyone (see signature) that is willing to work through all the details required.

 

[PoolguyinCT]

I look forward to checking it out.
There are several subscription and proprietary tools out there, with those considerations.

I’ll have to log on from a PC to view your sig and calculator, looking forward to it.

 

[mas985]

I look forward to checking it out.
There are several subscription and proprietary tools out there, with those considerations.

Maybe but I bet my price point is better.

 

[goldmaes]

I’m looking forward to the estimate. Which tool are you using? ASLA has several for public use.

A Water in transit vessel, without calculating can easily approach 3/4” daily evaporation.

Bucket testing is tricky as 4 vessels are present.
Bucket test will also be invalid, without draining below pool spill walls.
Pool, spa, surge tank & perimeter collection slot.

High water bills don’t guarantee a pool leak.

Water in transit pool leaks are a quite different, always start with the surge tank and the valves which isolate the vessels listed above.

Hopefully it is a true leak or no leak and not a design flaw.

This is exactly why I haven't done the bucket test. I'm confident here it would show 1/4" loss per day, but it discounts the overflow. The pool is 640 sq ft and it is raised 12" above grade. The water cascades down the weir wall on all 4 sides into trough that is approximately 12" deep by 6" wide. Water flows from the trough (gutter) back to the collection tank. I have tested the pool with the pump off and the pool and collection tank only loses the 1/4" to evaporation each day so I believe there is not a shell leak. I only seem to lose water when the pump is running which leads me to believe that there is a pressure side leak. What I don't know how to do is account for the thin layer of water going over the weir when the pump is on and how much additional evaporation would occur during the 9 hours the pump is running. I can't imagine that it could be an additional 1/2" of water per day.

 

[JamesW]

You're probably going to need to get the lines pressure tested.

If you're heating the water, that makes a big difference.

How much do you heat the water?

 

[PoolguyinCT]

This is exactly why I haven't done the bucket test. I'm confident here it would show 1/4" loss per day, but it discounts the overflow. The pool is 640 sq ft and it is raised 12" above grade. The water cascades down the weir wall on all 4 sides into trough that is approximately 12" deep by 6" wide. Water flows from the trough (gutter) back to the collection tank. I have tested the pool with the pump off and the pool and collection tank only loses the 1/4" to evaporation each day so I believe there is not a shell leak. I only seem to lose water when the pump is running which leads me to believe that there is a pressure side leak. What I don't know how to do is account for the thin layer of water going over the weir when the pump is on and how much additional evaporation would occur during the 9 hours the pump is running. I can't imagine that it could be an additional 1/2" of water per day.

unfortunately overflow channel are common culprits, which would leak more when system is engaged.
Though it is on the influent side, it is often mistaken for a return side leak, because it is charged when pump is on.

I could imagine an additional .5” on the high side, providing & hoping it is a well designed system.

Anything that touches water can leak. & one or more leaks can coexist with evaporation.


Clearly you are in an area with access to higher end contractors, a Lautner style pool hopefully would not be attempted by ham and eggers. those equipped to serve this market, should be easy to find.

As far as your research hitting dead ends, I’m not surprised. I can only think of 3 or 4 qualified guys authoring to your issues.

A competent leak detection company will have the tools to detect a gallon leaving that pool in 20 minutes. The detection equipment is sub $10k and is common & will compensate for evaporation.

Just don’t expect a water maintenance/ cleaning company to have these tools.

A contractor for this niche is well worth the investment.

 

[goldmaes]

You're probably going to need to get the lines pressure tested.

If you're heating the water, that makes a big difference.

How much do you heat the water?

I only occasionally heat the spa. I have never heated the pool.

 

[jatkinson]

Beautiful pool..... Just thinking aloud.... Aside from finding a competent contractor (which isn't always easy in florida) Is there anyway to isolate the waste drain, take your measurements and run it for a day? Even with the perimeter edge, it's december and you shouldn't be losing that amount of water. On the flip side, when the summer comes, you'll have so much extra water from the rains, you can sell it back to the water company.