Counterintuitive water loss

[Mizu]

Our garden pond (25x12x2, with membrane liner, skimmer and biofall) is in Southern California. The months of May and June were mostly cool this year with many overcast days. On several occasions the pond experienced overnight water loss of several inches. In contrast, July and August posted record heat during the day, plus unusual humidity for this area, but the pond saw almost no water loss, not even to evaporation (the pond is mostly shaded). However, in the last two nights of August, the air temperatures dropped significantly (10-20 degrees) below the temperatures in previous nights. Again, the pond experienced overnight water loss of several inches. It has been suggested that there may be a leak that closes in the heat (because something expands) and reopens when it gets cooler. (what could do that?) Or higher humidity may suppress water evaporation, allowing more water to evaporate when the air is drier. These are pure guesses. Water is precious in this region. Any help to explain the cause of this counterintuitive loss of water would be much appreciated. (An inspection did not disclose any of the usual sources of possible pond leaks.)

 

[sissy]

You say membrane liner is it 45 mil rubber liner .Do you know the temperature of your pond water .Dry air and even moist air can cause water lose of a couple of inch's .Have you checked for any wet spots outside the pond and have you checked you hoses for leaks

 

[MitchM]

Look up what the wind and relative humidity conditions were for the days/nights you lost water.

 

[j.w]

@Mizu

 

[Mizu]

You say membrane liner is it 45 mil rubber liner .Do you know the temperature of your pond water .Dry air and even moist air can cause water lose of a couple of inch's .Have you checked for any wet spots outside the pond and have you checked you hoses for leaks

 

[Mizu]

Thanks for the response. I am not sure of the thickness of the liner -- it should be what would be expected for a backyard pond--or water temperature (my water thermometer won't read). We have checked for wet spots or soft spots and found none. Same for leakage around the waterfall and skimmer and entry/exit pipes. The water is not overlapping the edges of the liner. The air temperatures here vary from 90 in the day to 60 at night at present. During the last two months, the air temperatures varied from 100+ during the day to 75 at night. The mystery, to me at least, is the loss of water when the air temperature dropped at night, something that did not happen when the air temperature was much higher at night. Has something contracted?

 

[sissy]

You can go any place and buy a regular outdoor thermometer and at least get a reading from that .Hot temps during the day and cooler nights can produce a fog off the pond that sucks water into the air and plants and wind have to be factored in .Splashing water is great for aeration but bad for loosing water

 

[Lisak1]

You have a puzzling situation there. I don’t think a shift from 90 to 60 degrees is enough to create expansion and contraction - both temps are still warm by definition. And most of your plumbing should be buried so it wouldn’t experience much temperature change at all. Water temps stay pretty consistent with those fast drops and rises so I don’t think it would be in the pond. Wind? Do you have a pet elephant drinking from the pond? Haha.

I’m gonna pond-er this one!

 

[Lisak1]

This may be a dumb question but there wouldn’t be anyone else putting water in that you don’t know about would there? Did you build this pond? Does it have an autofill?

Just thinking out loud. We were commenting one day that we hadn’t had to fill the pond for a long stretch and then our daughter said “but I put the hose I twice in July!” She topped it off when she noticed the pump chugging.

 

[sissy]

but you add in humidity and you can loose water .I have seen the fog over my pond in the early morning after a hot day with 98 % humidity and the cooler nights with high humidity and noticed the water lose .This is a brand new liner .I can loose at least and inch or 2 or even 3 because of high temps. and humidity in the air .