Prepared by
Global Environmental Solutions (GES)
Summary
Reservoir evaporation represents one of the largest continuous losses of stored freshwater across the United States. Collectively, the five reservoirs summarized in this report lose an estimated 460-610 billion gallons of water each year through evaporation along. As municipalities, agriculture, mining operations, power generation, and industry face increasing pressure on limited water resources, protecting stored water has become an increasingly important complement to conservation, infrastructure modernization, and water reuse.
This article is intended to provide a comparison of evaporation losses among well-studied reservoirs. The report is intended to support engineering discussions, strategic planning, and preliminary project evaluation. It is not intended for regulatory water accounting or legal water rights administration.
Introduction
Water scarcity continues to challenge municipalities, agriculture, mining, industrial operations, power generation, and environmental restoration throughout western North America. While infrastructure modernization, conservation programs, desalination, groundwater development, and water reuse remain essential components of long-term water security, evaporation from reservoirs and storage ponds represents a significant and frequently underappreciated source of water loss.
Unlike water demand, evaporation occurs continuously whenever atmospheric conditions favor vapor transfer from the water surface. High solar radiation, elevated temperatures, low relative humidity, persistent winds, and large exposed surface areas combine to produce substantial annual water losses across many western reservoirs.
Engineering solutions that reduce solar loading and wind-driven evaporation may complement existing conservation strategies while simultaneously improving water quality, reducing algae growth, minimizing wildlife interactions, and lowering long-term maintenance requirements.
This report summarizes published measurements and engineering estimates for fourteen strategically important North American reservoirs and presents a comparative assessment of representative annual evaporation losses.
Key Findings
- The five reservoirs summarized lose an estimated 460 – 610 billion gallons of water annually through evaporation.
- Lake Mead and Lake Mohave provide the highest-quality publicly available evaporation measurements because they are based on direct U.S. Geological Survey field observations.
- Reservoir evaporation varies considerably depending on climate, elevation, wind exposure, and reservoir geometry; therefore, site-specific evaluations are recommended when assessing water losses.
Reservoir Evaporation by the Numbers
Table 1. Representative Annual Reservoir Evaporation Estimates
| Reservoir | Approx. Surface Area
(sq mi) |
Annual Evaporation (ft/year) | Approx. Annual Water Loss
(Billion gal/yr) |
Primary Data Source |
| Lake Mead | 247 | 6.22 | 212–277 | U.S. Geological Survey (Energy Balance & Eddy Covariance) |
| Lake Mohave | 44 | 5.64 | 49–52 | U.S. Geological Survey (Energy Balance & Eddy Covariance) |
| Lake Powell | 254 | ~4.5–6.0 | 147–196 | U.S. Bureau of Reclamation Water Accounting |
| Lake Havasu | 31 | ~6.0–6.7 | 37–42 | Lower Colorado River Accounting / Bureau of Reclamation |
| Elephant Butte Reservoir | 57 | ~5.5–6.5 | 16–46 | Bureau of Reclamation Hydrologic Studies |
Although these reservoirs differ substantially in size and climate, they collectively demonstrate that evaporation represents a significant component of long-term water management. Even relatively modest reductions in evaporative losses can preserve billions of gallons of stored water over the life of a reservoir.
Free Preliminary Reservoir Evaporation Assessment
Every water body is unique. Climate, elevation, reservoir geometry, operating water level, wind exposure, solar radiation, and water temperature all influence annual evaporation losses.
GES provides free reservoir evaporation assessments for water storage assets for municipalities, engineering firms, mining companies, agricultural operators, industrial facilities, and water utilities.
A preliminary assessment typically includes:
- Estimated annual evaporation loss
- Estimated annual water volume lost
- Climate-based evaporation profile
- Preliminary evaporation reduction potential
- Initial evaluation of floating reservoir cover technologies
- Discussion of potential water quality and operational benefits
These screening assessments are intended to support early-stage engineering discussions and determine whether a more detailed reservoir-specific evaluation is warranted.
To request a complimentary assessment, simply provide the reservoir location, approximate dimensions, and available operating information to the GES team here.
Disclaimer
The estimates presented herein are based on published measurements, publicly available operational records, and engineering estimates developed by Global Environmental Solutions. They are not intended for regulatory reporting, interstate water accounting, water rights administration, permitting, or final engineering design. Reservoir-specific engineering studies should be completed before operational, regulatory, or capital investment decisions are made.
About Global Environmental Solutions
Global Environmental Solutions (GES) develops practical environmental technologies that help municipalities, industrial facilities, mining operations, agricultural producers, and infrastructure owners solve complex environmental challenges through applied engineering.
GES specializes in water conservation, reservoir evaporation reduction, dust suppression, erosion control, environmental remediation, water quality improvement, and specialty chemical technologies. By combining scientific research with real-world operational experience, GES develops solutions that improve environmental performance while reducing long-term operating costs. GES is committed to advancing practical, science-based environmental technologies that help customers improve operational efficiency while protecting valuable natural resources.
For additional information or to start a complimentary reservoir evaporation assessments please contact Global Environmental Solutions.