Google Trends comparison of the search terms "atmospheric water generator", "water from air", and "air to water".

[Text excerpted and adapted from Technical Bulletin No. 5 (revised 2023)—Environmental impact of widespread use of drinking-water-from-air systems issued by Canadian Dew Technologies Inc.This blog post supersedes two earlier blog posts on the same topic (My answers to questions asked in Oct. 20, 2020 Webinar: Introduction to Atmospheric Water and Impact on the atmospheric water reservoir from using water-from-air systems: an update) The human population keeps increasing and estimates have been refined of the atmospheric water reservoir volume.Concern has been expressed by some potential users of WFA systems that widespread use in a region could decrease the water vapour content of the atmosphere. If this was the case, would regional weather and climate be affected?Assessing Environmental Impact on the Atmospheric Water ReservoirEarth’s estimated human population is now 8 billion, projected to increase to 10.4 billion in 2100 (https://population.un.org/dataportal/home) so the 1993 worst-case impact estimate was updated as follows in the next paragraph, incorporating a revised per capita water consumption value of 50 L/day as suggested by Gleick (1998) for domestic water requirements (drinking, kitchen, laundry, and bath). Revised water cycle information was from Abbott et al. (2019).The atmosphere contains 12.9 × 10^12 m^3 of water or 0.001% of the Earth’s total water reservoir volume of 1.38 × 10^18 m^3. Water reservoirs include the atmosphere, ice and snow, biomass, surface water, underground water, and the oceans. Even if all 8 × 10^9 people on Earth used water from water vapour processors at the rate of 50 litres per day, they would consume only 0.003% of the available atmospheric water. In 2100, when population is expected to rise to 10.4 × 10^9, this worst-case impact would rise slightly to 0.004%.  Water vapour, the gas phase of water, diffuses along pressure gradients to zones of lower water vapour pressure. If a lot of water vapour was condensed into liquid water in a specific region such as a city, water vapour from outside the region would flow into the region. No net loss of atmospheric water vapour would be observed in the city.Water consumed for domestic water requirements does not exit from the water cycle. Within a day the water that is used or temporarily withheld from the water cycle would be returned to the environment to evaporate into atmospheric water vapour.

I trust you are enjoying your visit to Atmoswater Research and are gaining some valuable knowledge about water-from-air topics. Since 1999 the Atmoswater Research website has endeavored to provide the water-from-air community with accurate scientific & technical information---with a lot being free to access. Although consulting contracts, sales of digital goods, and advertising revenue give us an income stream it is far from being predictable and steady. Maintaining and improving this site requires a certain amount of cash flow. Therefore, we have added a "coffee jar" for those who would like to support us financially but do not have an immediate need for consulting services, digital goods, or an advertising spot. The "Buy me a coffee!" button is located on our home page, right-hand column (bottom; scroll down). Clicking the button below also opens the coffee jar which is a secure page in the PayPal system. Thanks very much for your support!-Roland Wahlgren 

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Participants at this well-attended webinar had lots of questions---too numerous to answer during the Q & A period at the end of the webinar. So the three panelists were asked to reply to a set of questions---the answers were sent recently to the registered attendees. Here are my answers to the set of eight questions assigned to me. They cover a variety of topics. I hope you find the answers interesting and useful.​

A Water-from-Air System Hourly Analysis Model for San Francisco, California is available as a free download on the Atmoswater Research website. During the prevailing California Drought, seventeen rural communities were identified by the California Department of Public Health as having "drinking water systems at greatest risk". Two of the affected counties, Sonoma and Santa Cruz are adjacent north and south respectively to San Francisco. Therefore, it is interesting to take a tour through the San Francisco hourly analysis model to see what it can tell us about the feasibility of using water-from-air machines (atmospheric water generators) as alternative or additional water resources in drought affected communities in Sonoma and Santa Cruz.

The Water-from-Air Resource Chart for Praia, Cape Verde (click to enlarge).

When designing drinking-water-from-air systems it is useful to know the limits to mechanical dehumidification efficiency. Mechanical dehumidifiers use chilled water coils, direct-expansion refrigerant coils or thermoelectric devices to provide a cooled surface over which flows the air to be dehumidified. Systems are designed usually with defrost controls to avoid frosting of the coil surface. Practically, the minimum temperature for coil operation is about 5 °C. The air leaving a wet coil is saturated so the state of leaving air may be, for example, dry bulb = 5 °C with 100% relative humidity. This combination of temperature and humidity is associated with air having a water vapour density (WVD) of 6.8 grams of water per cubic metre of moist air. The blue curve in the chart below shows how efficiency of water collection varies depending on the water vapour density of the ambient (entering) air.Let's use an example to explain how the curve was constructed. Ambient air at standard testing conditions of 26.7 °C, 60% relative humidity enters the dehumidifier (atmospheric water generator). At standard atmospheric pressure of one atmosphere (1.013 bar), psychrometric calculations show the ambient air is capable of holding 15.3 grams of water vapour in a moist air volume of one cubic metre. As this unit volume of air flows across the 5 °C chilled surfaces of the coils the mass of condensate collected =  (15.3 g per cubic metre - 6.8 g per cubic metre) x 1 cubic metre = 8.5 g. The table below shows a series of similar calculations encompassing the natural range of water vapour densities in the atmosphere at the Earth's surface (about 4 to 22 g per cubic metre).Ambient temperature together with the refrigeration capacity of the dehumidifier will determine whether or not a chilled surface temperature of 5 °C can be achieved. Therefore, the chart also has efficiency curves for leaving air at 10 °C and 15 °C. In Belize City air temperature was about 32 °C and the 40 Ton refrigerant capacity machine I was testing for my client had a leaving air temperature (similar to coil temperature) of 16 °C. Efficiency of water production was about 45%, near the limit of what could be expected given the weather conditions and equipment capacity. The atmospheric water generator (about the size of a 20-foot shipping container) was producing drinking water at the rate of about 2500 L/day—its designed capacity.Note: You may click on the chart and table to enlarge them.