Does anybody know approximently how much water an inground pool (420 sq ft) will lose due to evaporation during the winter in Arizona? I did a search but couldn't find anything. Thanks
Evaporation
- Thread starter meatloaf
- Start date
- May 3, 2007
- 16,815
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
There are a lot of factors involved with estimating evaporation. If you use a solar cover, it should be almost zero. If you use a heater without a cover, it will be quite large.
If you don't have a cover and no heating, plus the water temp is about 52 deg F and fairly little wind, then I would estimate evaporation to be around 0.1"/day. But that is based upon a few other assumptions such as full sun exposure.
If you don't have a cover and no heating, plus the water temp is about 52 deg F and fairly little wind, then I would estimate evaporation to be around 0.1"/day. But that is based upon a few other assumptions such as full sun exposure.
Map of annual evaporation rates (in inches):
http://www.grow.arizona.edu/images/water/panevap.gif
You'd expect the bulk of it to be in the summer, of course. You could try poking around that website and see if they have data broken down by month, or something.
--paulr
http://www.grow.arizona.edu/images/water/panevap.gif
You'd expect the bulk of it to be in the summer, of course. You could try poking around that website and see if they have data broken down by month, or something.
--paulr
Just a personal observation, but it seems that I lose more water during dry windy periods, than during hot, humid, still days.
That makes perfect sense. The formula for evaporation from pools has a factor for wind and another for the difference between the saturation vapor pressure (at water temp) and the actual vapor pressure (at air temp). So there is more evaporation with more wind and with dryer warmer air and with warmer water temperature. The sun does not directly cause evaporation, but it indirectly increases it by warming the temperature of the surface of the water.jparr said:
Here are some specific examples.
Water Temp: 85ºF
Air Temp: 75ºF
Relative Humidity: 66%
Wind: 0
Evaporation: 0.20 inches/day
Same as above, but with wind of 5 MPH: 0.62 inches/day
Save as above, but with wind of 10 MPH: 1.06 inches/day
NOTE: wind is measured near the water surface so is generally lower than general wind speed
Same as above (no wind), but with relative humidity of 20%: 0.32 inches/day
Same as above, but with water and air temp at 50ºF: 0.04 inches/day
The evaporation rate during the day and at night is actually somewhat similar (assuming the same wind) because the relative humidity rises at night as the temperature cools, basically keeping the same amount of water in the air. You just see the evaporation effects more readily when the air is cooler since its increased saturation means there will be more visible "steam" as the water condenses.
Glad I found this discussion. I was thinking that maybe there is a leak somewhere. After all the rain and wind storms that we got in northern California during the past few months, I did not expect the water level in the pool to be 1' to 1.5" lower than normal. There is an auto fill but it was turned off for the winter assuming that it was not needed. After reading this info on evaporation, I need to make sure that it is turned on in the winter when it gets windy.
I just saw this. I live in NW Florida, in the panhandle, and I had noticed quite a drop in the water level of my pool. It has been very sunny and windy lately, so could this be it? I did fill it about a half an inch, then like I said, it got windy, next thing, I noticed it dropped another inch! The mornings are a little cooler, and I do see the evaporation rising from the pool, so I hope this is it. Never noticed the water level drop like this before, and we haven't been in the pool since September.
Welcome to TFP! 
You can do a bucket test as described in the Pool School article Leak Detection to make sure you don't have a leak.
You can do a bucket test as described in the Pool School article Leak Detection to make sure you don't have a leak.
I always use a bucket test to make sure of leaks like chem geek mentioned but there is also this online thingy to gauge evaporation
http://www.leaktools.com/professional/evaporation.php
http://www.leaktools.com/professional/evaporation.php
In the process of doing the bucket test, but I did the online thingy ("0) and was quite surprised at the results! checked the weather forecast on weather underground for that period of time, and the water evaporation was pretty high in comparison to what it would be like on a day like today. Thanks for that! I'm sure the results are just going to show it was evaporation "0)
