Evaporation Retardation — Helping Surface Supplies Stay Put

By Charlie F. Anderson

Are chemical evaporative retardants a good method to prevent losses from reservoirs?

Water is the universal solvent and the underpinning of developed economies — a precious resource that we literally can’t live without.

Water use trends indicate that less is being used now than in 1975. According to a 2009 United States Geological Survey report[1], for the first time in decades the total water use (in 2005) was lower than it was in 1975, and per-capita water use was lower in 2005 than it has been since the 1950s. Much of this reduced use is due to better awareness of the need to manage water resources more effectively, and implementing water conservation measures, improved technology, and legislatively-mandated low-water-use fixtures in new construction.

Yet that is not the end of the water resources story; water resource professionals still face more stressing news and issues. Even with more awareness and best conservation practices, water resource management remains a hot topic due to the fact that water is a limited resource and mounting pressure from population increases. For a variety of reasons, the U.S. population is migrating away from water-rich states to states in the arid and semi-arid Sun Belt and Southwest. A recently published American Water Works Association (AWWA) report[2] surveyed 485 utilities from zero to 5,000 connections to more than 150,000 connections. The reporting utilities were 90 percent public and 10 percent private. The report showed drought and periodic water shortages as the eighth-most-important issue facing water professionals.

As evidenced by a 2009 USGS report, water sector professionals have done a good job of implementing sustainable practices, triple-bottom-line business models, sound science and engineering practices, water conservation rate structures, and water efficiency and conservation measures to better preserve water resources.

So the question is: Do we have any other tools in our tool box to help improve our water resource management and preservation?  The answer is … maybe. 

What constitutes the maybe? One significant area of water loss for utilities that depend on surface supplies is evaporation. Yet little has been done to provide a good repeatable, sustainable way to retard evaporative losses in surface supplies.

In a recent AWWA Journal paper[3], the Southern Nevada Water Authority (SNWA) reported on the performance of a proprietary monomolecular evaporative suppressant composed of a mixture of steryl and cetyl alcohols and calcium hydroxide. When applied as a dry powder to water surfaces, the chemical quickly disperses and spreads on the surface forming a monolayer film, which has been shown to retard evaporation. Although the journal article was not conclusive about the potential for large-scale use of similar evaporative retardants, it did report several key and promising findings. First, it indicated that the monolayer evaporative suppressant tested in controlled evaporation pans saved water when compared to a control with no evaporative chemical. Treatment containers averaged 30 percent less evaporative loss, and they ranged from 18 to more than 51 percent reduction in evaporative loss. The field trial applying the chemical to a small residential lake, Lake Sahara, did not show statistically significant savings, but the authors speculated the suppressant’s use may have saved significant volumes of water during the trial. And finally, the SNWA results of water quality testing found no evidence of either short-term limnological health threats or environmental concerns arising out of the use of the chemical suppressant.

Many other jurisdictions and agencies between 1964 and present have investigated the efficacy of chemical evaporative retardants in drinking water surface sources. Among those are Australia[4]^,[5], Singapore’s Public Utilities Board[6], Kingdom of Saudi Arabia[7], Sandia National Laboratories[8], and the Texas Water Commission[9]. These investigations and the recent SNWA study point to the potential for chemical evaporative retardants to save significant quantities of water lost to evaporation.

Why is this important? It is important because climate variability, population migration to less water-rich states, and increasingly more frequent drought in the U.S. is pushing water resources to the limit. Every drop saved can make a difference. The following U.S. Drought Monitor map indicates the severity of drought and water stress (darker color = more severe) in the continental U.S. as of May 2014. It also illustrates that the most drought-stricken areas are in states that have experienced large population increases that are placing even more stress on their limited water resources.

Drought conditions in the continental U.S. (Credit: National Drought Mitigation Center)

Evaporative retardant chemicals are available in today’s marketplaces that have received U.S. EPA approval for use in raw water resources that serve as sources of drinking water.

These chemicals may provide another tool for water professionals to better preserve source water resources. Perhaps this article will compel utilities and researchers to jump in and pilot full-scale investigations in large surface lakes and water sources to answer whether or not these chemicals can truly provide another important tool for utilities in todays stressed water resource environment.

Charlie Anderson of CDM Smith has served as the director of utilities and deputy city manager for Arlington, TX, and was on the American Water Works Association (AWWA) Board of Directors for six years until his term as Immediate Past President ended at the conclusion of AWWA’s 2014 annual conference in Boston, MA.