Slowly losing water in a completely covered pool?

[rlab]

I have had the pool continuously covered for the last 2 weeks with a thermal foam cover that is completely impermeable (i.e. not a mesh cover). The cover is tight fitting edge to edge, covers 100% of the pool surface. Daytime ambient and pool temps are hovering around 50F.

When doing a check today I was surprised to see water level had dropped about a 1/2 inch in 2 weeks. Equates to about 40 gallons of water loss per week.

I was expecting the cover should mean close to zero water loss, but is that realistic?

Also how would I do a leak detection test in this case? I can't really do the bucket test with the cover in place.

 

[jetola]

You should do the bucket test, to determine if you have a leak. Leave the cover off for 48 hours while you do the test. It will tell you for sure if you have a leak. 1/2 inch in 2 weeks is not much - its basically 1 millimeter per day. Could easily be evaporation, event with a cover.

 

[rlab]

Heh yes good point, didn't think of just leaving the cover off for the test.

I would probably need to leave it for a good week or so for there to be a noticeable difference? I assume a 2mm difference over 48 hours is not really perceptible with the bucket test?

 

[woodyp]

1/2 inch in 2 weeks is neglidgeable.

 

[PoolGate]

I don't think you can stop evaporation with the cover you describe. It would need to be like hermetically sealed to stop all evaporation.

 

[rlab]

I have been doing the bucket test with cover off pool, and after a 5 day period there is about a 1/4 inch difference.

However the pool surface is exposed to different water currents, sunlight and wind conditions to the water in the bucket. So I'm thinking that may account for the difference?

I can't find any info on how big a difference would indicate a leak with the bucket test? Advice just seems to be that *any* difference indicates a leak?