Borates & Evaporation rate

[timjwilson]

Hoping this is not too dumb a question. I am considering adding borates to my pool. I've studied all the stickies, etc. and am confident I understand the process. I do have one question I have not seen addressed: it seems that borates affect the surface tension of the water (I've seen posts where folks have mentioned that the meniscus goes away). Given that, is there any chance that borates will affect (increase) the evaporation rate? I live in Tucson where water is somewhat precious and I wouldn't want to do anything that would add to my water use.

 

[pooldv]

Welcome to TFP!

I have never seen any discussions along these lines and have not experienced anything noticeable in my few years of having borates in my pool. But, the last two years have been rainier vs the several years of drought before that.

 

[JoyfulNoise]

Hoping this is not too dumb a question. I am considering adding borates to my pool. I've studied all the stickies, etc. and am confident I understand the process. I do have one question I have not seen addressed: it seems that borates affect the surface tension of the water (I've seen posts where folks have mentioned that the meniscus goes away). Given that, is there any chance that borates will affect (increase) the evaporation rate? I live in Tucson where water is somewhat precious and I wouldn't want to do anything that would add to my water use.

There is little, well-defined data on this effect. Posts related to the changes in surface tension used methods of measurement that are not standard laboratory methods and thus are really more of a qualitative demonstration of the effect and not at all quantitative. Surface energy values are always measured relative to the surface that the fluid is in contact with and the change in liquid/gas surface energy (surface tension of the fluid in contact with air) is likely to be vanishingly small as to have little to no effect on the rate of vaporization. Adding salts of any kind shifts a fluids boiling/freezing point which is a much larger effect and not related to surface tension.

I live in Tucson as well and I have had pool water with no borates and 50ppm borates in the water and I can say definitively that the only thing that affects the evaporation rate of water is when I use my bubble cover or not. If you're concerned with water conservation, keep your pool covered and you can practically drive your pool water evaporation to zero.