Taxation of Evaporation

Taxation of Evaporation

How much water could the lake possibly lose to evaporation?

Photo submitted by Steven Shields

Probably more than you think.

It may not seem feasible, but evaporation can be measured, and the Brazos River Authority produces a report each year with the estimated water loss. Why should you care? Well, if you live on a lake or enjoy water skiing on a water supply reservoir, it’s important to keep in mind that water levels fluctuate even when nothing is seemingly happening. 

It’s not like you can see it. 

Evaporation is the change from liquid water to water vapor. Water from the Earth moves from the surface to the atmosphere via evaporation.  

“Evaporation occurs when energy (heat) forces the bonds that hold water molecules together to break. When you’re boiling water on the stove, you’re adding heat to liquid water. This added heat breaks the bonds, causing the water to shift from its liquid state to its gaseous state (water vapor), which we know as steam.” – U.S. Geological Survey.

It’s an important part of the water, or hydrologic, cycle – water makes it way from the Earth’s surface to the atmosphere and back again.

“Water molecules can take an immense variety of routes and branching trails that lead them again and again through the three phases of ice, liquid water, and water vapor. For instance, the water molecules that once fell 100 years ago as rain on your great-grandparents’ farmhouse in Iowa might now be falling as snow on your driveway in California.” – NASA 

So, what does the traveling of water have to do with your local lake?

Well, evaporation often consumes twice as much water as the total used by cities, industry, agriculture, and mining concerns from the Brazos River Authority system of water supply reservoirs. Plus, the bigger the size of the surface of the body of water also means the larger the amount of evaporation to occur.

It’s important to understand evaporation when you’re wondering why the water level seems to be dropping or more underwater hazards seem to be appearing. 

Evaporation is a constant, natural part of the water cycle. The loss of more than 500,000 acre-feet of water in 2021 was due to evaporation, compared to the roughly 240,000 acre-feet of water used by municipalities, industrial, irrigation, and mining combined. In 2020, the total water use from the BRA system of reservoirs was 288,968 acre-feet. In comparison, the total evaporation loss from the system was measured at 540,244 acre-feet, nearly twice the amount.

As temperatures rise, increased demand by residents, agriculture, cities, industry, power plants and others on water stored can also draw down a lake’s level. This impact is made worse during periods of extended drought when water entering reservoirs is lowest.

There are some ways that you can alleviate evaporation’s effects during everyday chores. When not in use, place a pool cover over your pool to reduce evaporation loss. When watering your plants during the summer, try watering when the sun is down, as it can greatly reduce the amount of water that is lost to evaporation.

Though it can be frustrating for those who live near Texas lakes or turn to them for recreation, fluctuating lake levels are a sign that reservoirs are successfully supplying water to thirsty Texans during times of need and that the water cycle is still turning its wheels.