Does a 1000 SF of Grass use more Water than a 1000 SF of Pool?

[Chuckiechan]

I was having a discussion with a person at a party, and this question seemed one that needed to be answered.

I suspect it might be true, but there are a lot of variables. So we should assume for starters, daily watering with no run off, vs a pool with no cover, and no external heat added.

Any ideas on this?

 

[JoyfulNoise]

It's roughly the same. Pools will evaporate about 1/4" per day and, according to the source below, a moderate water use grass will evapotranspirate about 6 to 8 mm/day

https://www.usga.org/content/dam/usga/pdf/Water%20Resource%20Center/turfgrass-water-requirements.pdf

 

[Chuckiechan]

That was my argument. Thanks for that!

 

[Steve_in_C]

At times a pool may evaporate more. Plants have small pores (stomata) which are able to open/close to affect the rate at which they transpire gases. Closing these stomata slows metabolism of the plant since gases needed such as CO2 and H20 are limited. Stomata can close to conserve water during a drought for example. The soil moisture at the ground surface would be less during a drought further decreasing evaporation. A pool on the other hand would likely evaporate more during a drought due to lower relative humidity. So under normal conditions there may not be difference between a pool and grass. But under the right conditions, the grass may use less water.

Irrigation is a whole other issue. You are not just watering the area under the sprinkler, the unwatered soil adjacent to the irrigated area will wick away much water (capillary action). So a 1000 ft2 pool may use much less water than 1000 ft2 of irrigated grass under irrigated conditions.

 

[AUSpool]

Grass has a greater surface area than a pool surface, but at the end of the day this will offset the bio nature from above and the end result will be much the same as that from Joyful's observation. However, if your not watering your grass and still topping up your pool than the outcome is obvious.