Water Evaporation

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 Joined: Tue 11 Sep, 2007 07:51
Water Evaporation
How do I measure water evaporation? This morning after getting up I found water levels below the skimmer line... the motor for the surface is then not pulling in water. How do I know how long it takes to fill 1 inch or 2 inch in a 16 x32 [1/2 of which is 4 feet... the other 1/2 graduating to 8 feet] in terms of mins or hours? I close the motor as I did not know how long it takes to fill 1 inch of water for the 21,00023,000 gallons. Advise

 Pool Industry Leader
 Posts: 2381
 Joined: Thu 21 Jun, 2007 21:27
 Location: San Rafael, California
The easiest way to measure the rate of water evaporation and to ensure that it isn't a leak is to take a bucket of pool water and put it next to the pool exposed to the same sun and wind conditions as the pool. Measure the distance from the water in the pool to some known level such as the bottom of the coping or a mark in the tile. Do the same for the water in the bucket, say from the water level to the top of the bucket or a marking in the bucket. If both levels drop about the same in a day (or several days), then this is just from evaporation. If the pool level drops significantly more, then you probably have a leak.
This website has a map that will give you a rough idea of evaporation rates. Most evaporation occurs in the summer months so if you take the annual rate, say 50", from the map, then divide that by half a year, or 182 days to get 50/182 = 0.27" per day as a rough expected evaporation rate.
As for how long it takes to fill the pool back up, that depends on the flow rate from however you are filling the pool. The depth of the pool does not matter. 1" of water in an area of 16' x 32' is 16x32x(1/12) = 42.67 cubic feet which is 319 gallons. A typical garden house attached to your house water supply will output around 10 GPM so it would take about 319/10 = 31.9 minutes or around a half hour to fill your pool by 1". You can measure your actual GPM rate from your hose by timing how long it takes to fill a bucket of known size  say a 2gallon bucket. If it's 10 GPM, then it will take 2/(10/60) = 12 seconds to fill. GPM = 60* (Bucket size in Gallons) / (Time to fill bucket in seconds).
Richard
This website has a map that will give you a rough idea of evaporation rates. Most evaporation occurs in the summer months so if you take the annual rate, say 50", from the map, then divide that by half a year, or 182 days to get 50/182 = 0.27" per day as a rough expected evaporation rate.
As for how long it takes to fill the pool back up, that depends on the flow rate from however you are filling the pool. The depth of the pool does not matter. 1" of water in an area of 16' x 32' is 16x32x(1/12) = 42.67 cubic feet which is 319 gallons. A typical garden house attached to your house water supply will output around 10 GPM so it would take about 319/10 = 31.9 minutes or around a half hour to fill your pool by 1". You can measure your actual GPM rate from your hose by timing how long it takes to fill a bucket of known size  say a 2gallon bucket. If it's 10 GPM, then it will take 2/(10/60) = 12 seconds to fill. GPM = 60* (Bucket size in Gallons) / (Time to fill bucket in seconds).
Richard
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