What is atmospheric water generation & how has it evolved?
Ten years ago, the United Nations declared that every individual on our planet has the right to clean, fresh and safe water (1). Unfortunately, the World Health Organization (WHO) estimates that one in three people globally do not have access to safe drinking water with 10% of the population lacking basic drinking water services. Safe drinking water also requires adequate sanitation services to prevent source waters from becoming contaminated. The WHO estimates that lack of adequate sanitation affects about 1.8 billion people or 25% of the world’s population (2).
In many developed regions of the world, drinking water is generally considered safe. However, even safe drinking water may contain contaminants with known or unknown health effects. In the U.S., the U.S. EPA currently regulates 91 known water health-related contaminants in municipally treated water supplies (3). These contaminants range from microorganisms to disinfectants and their byproducts to organic and inorganic chemicals, radionuclides, and heavy metals like lead. The EPA also has multiple lists of suspect contaminants under review (Contaminant Candidate List (CCL)) (4). These supplemental lists include a growing number of emerging potential contaminants such as perfluorinated compounds (PFAs), persistent organic pollutants (POP), endocrine disrupters, pharmaceuticals, personal care products, premise plumbing pathogens (OPPP) like Legionella, and others. Unfortunately, the process to review each possible contaminant is time consuming, taking multiple years.
Large municipal water systems typically meet water treatment contaminant regulations. However, small systems providing water to fewer than 3,000 people and very small systems, providing water to fewer than 500 people, have a more difficult time achieving regulatory goals, and private wells are not regulated or monitored at all. To help consumers understand more about their water quality, the Water Quality Research Foundation published a contaminant occurrence map (5) for the U.S. showing 57 primary and secondary drinking water contaminants.
Concern about contaminants in drinking water, as well as taste preferences and issues of convenience have resulted in bottled water becoming the drink of choice for many consumers around the globe. Given the amount of plastic pollution generated by bottled water consumption, is it really the best alternative to municipal water sources, especially in regions without a ready supply of fresh water?
What Are Atmospheric Water Generators?
There is a disruptive technology emerging in the marketplace that may provide a better choice: atmospheric water generators (AWG).
Consider the fact that there is virtually an unlimited supply of drinking water in the humidity of our air. Earth’s atmosphere contains 37.5 million-billion gallons of water (6) while the world’s population uses about 5.2 billion gallons of water per day (7) (about 70% of that is used for agricultural applications). Thus, the impact of harvesting atmospheric water for drinking water by AWG is negligible.
Atmospheric water generators potentially can produce at the point-of-need fresh and environmentally friendly water without the plastic waste or carbon footprint of bottled water. For those relying on municipal water supplies with potential drinking water contaminants, especially contaminants due to aging infrastructure like lead pipes, AWG offers a means to disconnect from traditional water supplies.
Of course, pulling water from air does not guarantee the water is free from contaminants, especially from particulates and lead. The list of air pollutant contaminants (8) regulated by the U.S. EPA is small compared to that of municipally supplied drinking water. Conceivably, this list of air contaminants is woefully inadequate when it pertains to drinking water.
This means that AWGs must be designed to prevent airborne contaminants from being present in the produced drinking water. System designs should include multiple barriers to prevent airborne contaminants, including point-of-use drinking water treatment technology and disinfection methods like ultraviolet light to ensure water safety. Further, the materials used to construct AWG systems must be safe and must not leach contaminants into the product water.
Cooling Condensation vs. Wet Desiccation
There are two major technologies used in commercially available AWGs: cooling condensation and wet desiccation. Cooling condensation AWG technology (Fig. 1) operates similar to a dehumidifier. The air temperature is cooled below the dew point, resulting in the condensation of the atmospheric water vapor, which is then collected.
Wet desiccation water generation (Fig. 2) deploys a concentrated brine solution to adsorb water which is then extracted by heating the desiccant followed by cooling to condense the water.
Relative humidity of the air and air temperature are the primary determinants governing the efficiency of water generation by AWGs. Generally, the greater the atmospheric humidity and the warmer the air temperature the more efficient the water production.
There are also new technologies under development. An emerging technology developed by the University of California-Berkley (8) uses metal organic framework (MOF) technology to extract water from the atmosphere. The MOF chemistry is designed like a lock and key, meaning that in theory, only the water molecule can be captured and held. The MOF pore diameter is small enough to exclude large molecules of pollutants (such as benzo(a)pyrene) and selective enough to preferentially bind molecules of water over CO2, NOx, SOx, etc. Thus, the potential for inclusion of airborne contaminants is reduced, as the MOF chemistry is specific for capturing only water. The MOF is then heated with the resultant water vapor cooled and condensed (Fig. 3). Unlike other AWG technologies, the MOF chemistry is reported to capture water at the levels of relative humidity and temperatures found in deserts, which is 7% relative humidity and 27°C (9).
AWG technologies are energy intensive, with many deploying solar energy to power the equipment or drive the water harvesting process. Figure 4 shows the approximate energy cost for three different classes of AWG systems: a classic refrigeration represented by Genny (Watergen), a combination of solid sorbent and solar thermal system represented by Source (ZeroMassWater), and a combination of solid sorbent and refrigeration represented by WaHa (Water Harvesting Inc). Many systems are deployed as “central systems” in communities where water is scarce.
Water Quality & Product Certification
Atmospheric water generators for drinking water consumption must be certified free of potentially harmful contaminants either captured from the air or leaking from their materials of construction. Most important, the AWGs must produce drinking water that is microbiologically safe.
Lastly, these products must perform as stated, which means that product certification to an internationally recognized testing and product performance standard is mandatory. To that end, the International Association of Plumbing and Mechanical Officials (IAPMO) developed an American National Standards Institute (ANSI) and American Society of Safety Engineers (ASSE) International Standard that addresses the performance and materials of construction of AWGs; IAPMO/ASSE Standard 1090-2020 “Performance requirements for drinking water atmospheric water generators.”
Key components of the certification—in addition to material safety—include daily production rate, energy efficiency, microbiological safety and performance testing of any integrated filters included in the system design.
Atmospheric water generators could potentially be a solution for those lacking the basic human right to clean, fresh drinking water. Strategic deployment of AWGs in water-starved areas is potentially the first step to water freedom for the local populous. For those on municipal systems with inherent water quality issues such as those due to decaying infrastructure, AWGs offer the option of disconnecting from the local water supply. Of course, challenges lie ahead for this technology, especially in terms of energy consumption and water production efficiency. However, if those challenges are met, this technology is primed to make a disruptive impact on the future of drinking water availability.
- United Nations Declaration as Water as a Human Right: https://www.un.org/waterforlifedecade/human_right_to_water.shtml
- Today’s Environmentalist: https://todaysenvironmentalist.com/2019/07/12/1-in-3-people-globally-do-not-have-access-to-safe-drinking-water/
- U.S. EPA Primary drinking Water Regulations: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
- U.S. EPA Contaminant Candidate List and Regulatory Determination: https://www.epa.gov/ccl
- Water Quality Research Foundation Contaminant Occurrence Map: https://www.wqrf.org/map.html
- The Weather Guys – How much water is in the Atmosphere?: https://wxguys.ssec.wisc.edu/2018/02/05/water-in-atmosphere/
- The World Counts: https://www.theworldcounts.com/stories/average-daily-water-usage
- U.S. EPA Critical Air Pollutants: https://www.epa.gov/criteria-air-pollutants
- Hanikel, N. and M.S. Prevot, F. Fathieh, E.A. Kapustin, H. Lyu, H. Wang, N.J. Diercks, and O.M. Yaghi. “Rapid Cycling and Exceptional Yield in a Metal-Organic Framework Water Harvester”. ACS Central Science 2019, 5, 1699-1706.