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Thread: Does Pool Water Evaporate While Covered?

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  1. #1
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    Default Re: Does Pool Water Evaporate While Covered?

    It's a black winter cover, and the area gets sunlight for many hours each day - no trees, no really tall houses around it - when I reach my hand into the skimmer the water at the top feels HOT.

    When I had the leak, there was one spot outside the pool that was REALLY wet - but when I checked last week, the ground is damp all the way around the pool - not really wet in any particular spot - but damp everywhere. That wouldn't IMO correspond with a leak.

    I'll probably open the pool this week and hope for the best. I was just thinking that the sun beating down on the black cover might have caused the water to begin evaporating at a faster pace since it's warmed up these past two months - and since it's not a solar blanket, but a cover that overhangs the pool, it seems possible that water could indeed evaporate and escape. But who knows!

  2. #2
    markphin is offline Registered+ Thread Analyst markphin 1 star
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    Default Re: Does Pool Water Evaporate While Covered?

    If your winter cover actually lays on the water, your cover may have some small holes or be worn enough to allow water to pass through. The weight of the cover itself on the pool coupled with any rain water on top of it will allow water to pass through any holes on the cover until there is equal foces on top of the cover as underneath. as the water on top of the cover evaporates the cover will continue to allow water to pass through until all is in equalibrium again. The best way to tell is to observe during a prolonged dry spell and see if your cover has any free standing water on it. If so, your cover is leaking.
    Hope this helps.

  3. #3
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    Default Re: Does Pool Water Evaporate While Covered?

    3" in 2 months. I wouldnt lose any sleep over it. Open the pool and try to measure a loss in 1 week.

    You may be surprised to know that your plastic winter cover will actually allow water through on a micro basis given enough time.

    If you have rain water lying on your cover, it will exert pressure on your cover and you actually may have a little water seep up through and evaporate.

    I'd turn on the hose for a few hours to gain the lost water and start swimming.

  4. #4
    docsobeck is offline PF Supporter Thread Analyst docsobeck 0
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    Default Re: Does Pool Water Evaporate While Covered?

    i can attest to the "water through the cover" theory. i used to panic about how much my water level went down over the winter (inground pool, solid cover). i would leave the water level up at closing (late september), and it would be down a foot and a half at opening (late may). i kept thinking that there just HAD to be a leak, but i wasn't losing water during the summer. since i pump water off the cover several times a winter, someone finally pointed out that i was probably pumping out pool water since there was some "pass through equilibrium" going on.

    sure enough, my old cover was starting to get ratty so i put a brand new one on last fall, and i still had water loss, but not nearly as much.

    if you take a look at how those covers are really made, it's not all that surprising. they're basically woven from strips of plastic, and the weave allows water to pass through very, very slowly.

    not to worry... you could EASILY have lost 3" from pass-through.

  5. #5
    waste is offline PF Support Team Whizbang Spinner waste 3 stars waste 3 stars waste 3 stars
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    Cool Re: Does Pool Water Evaporate While Covered?

    Susan, it seems to me that water's first two priorities are; 1) to seek it's own level or the lowest place it can get and, 2) Evaporate, ie - leave the place it's worked so hard to get (somewhere further down it's agenda is to give life, esp. to algae) What I've noticed on the many pools I've worked on is that a hole in the cover is the prime suspect, if you have one and try to pump the water off your cover, you will lose pool water (however, the faster you pump off the cover, the less pool water you'll lose). I can't question that some water may make it through a 'holeless' cover, but I think the amount would need to be measured with a well calibrated micrometer.
    So I offer this other scenario:
    When you get water from precipitation on top of the cover the overall level of the pool water is raised (both above and below the cover). Water in a pool freezes from the top down. Only the top ~10% of an iceburg is above water. If the water on top of the cover freezes, it will try to 'sink' into the pool, forcing the still liquid water up and possibly over the top edge of the pool. Since water expands when it freezes, when it melts you will finally notice that you've lost some water. (This isn't as elloquent as I might like, but should do for starters) In short, don't worry too much about the 3 missing " of H2O, until you notice a 'larger than expected' drop in the pool water after running it.
    Luv & Luk, Ted

    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill libraries

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