Registration is now open for the "Atmospheric Water, Part 3" Webinar on November 17. The registration page is at ​http://bit.ly/SGC-Nov17

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.​

• ​What effect will widespread global atmospheric water use have on the world climate?   

The big picture is the water cycle. Every moment, myriad processes, natural and human-caused, are evaporating and condensing huge amounts of water. Liquid water that humans consume for drinking is only temporarily with-held from the water cycle (hours or days). The atmosphere contains 15.5 million million cubic meters of water according to a 1995 report by the American Geophysical Union. Various natural processes already transport and distribute vast volumes of water vapor and liquid water across Earth. Even if every single human alive in 2050 (using the UN's 2007 projection for a population peak of 9,200 million people) used water from water-from-air machines at the rate of 50 L (0.050 cubic meters) per day, they would consume (temporarily) only 0.003% of the available atmospheric water. This scenario involving the entire human population is unlikely, so it is also unlikely that water-from-air technologies will cause a drier atmosphere in the context of the Earth’s water cycle and natural processes of water transport and distribution.

Water vapor, the gas phase of water, diffuses along pressure gradients to zones of lower water vapor pressure. If a lot of water vapor was condensed into liquid water in a specific region such as a city, water vapor from outside the region would flow in immediately. No net loss of atmospheric water vapor density would be observed in the city.

Water consumed for domestic water requirements does not exit from the water cycle. Within a day or so the liquid water that is used or temporarily with-held from the water cycle would be returned to the environment by evaporating into atmospheric water vapor.

On a clearly bounded terrestrial surface such as a tropical island, atmospheric water vapor processing systems would increase slightly the annual precipitation. Let us say a large-scale AWG array is installed on an island such as Grand Turk (Turks & Caicos Islands). The island has a surface area of 18 square kilometers (1,800 ha). The AWG array produces water from the air at a rate of 75,335 cubic meters annually. This is equivalent to a rainfall of 7,533 mm over one hectare (10,000 square meters). The average annual precipitation of Grand Turk is 604 mm. This value would be enhanced by [7,533 mm/ha/1,800 ha] = 4 mm (or 0.7% annually, an amount less than the natural variability from year to year. The annual total precipitation in the year 2000, for example, was 704 mm.  

To reinforce the fact that long-term human direct impact on atmospheric water is negligible, note that dehumidifiers and air-conditioners dripping condensate have been increasingly used since the 1950s. I used NOAA global specific humidity data (measured in grams of water per kilogram of air) and subtracted the earlier 30-year 1951 to 1980 annual field from the  more recent 39-year 1981 to 2019 field. The resulting map showed several pools of higher specific humidity (+2 g/kg). These are likely related to climate change. Drying of about -2 g/kg is noticeable over the Sahara and Gobi deserts---more likely to be related to climate change than use of HVAC equipment. Over most of Earth specific humidity has been remarkably stable (+/-1 g/kg) for the past seven decades. By the way, I posted the map in the Atmoswater Research blog. Indirect environmental impacts are more likely. These will be related to the materials used in manufacturing AWGs, product life cycle aspects, and so on. Also, AWGs will enable humans to expand their footprint which could increase population density in a region, lead to increased sewage and waste disposal challenges, and increase energy use. 

These analyses indicate widespread global atmospheric water use will not noticeably affect the world climate.

• How does the cost of atmospheric water compare for a drinking water source as compared to more conventional sources?

In a tropical climate where a chilled-coil AWG produces water at its rated capacity every hour of the year the electrical energy cost of the water will be, on average, about 0.4 kWh per liter (400 kWh per cubic meter; 1.5 kWh per US gal).

More conventional sources of water have these electrical energy costs:
- Surface water, public supply: 0.37 kWh/cubic meter (Young, 2014)
- Groundwater, public supply: 0.48 kWh/cubic meter (Young, 2014)
- Tap water, 0.46 kWh/cubic meter (Gleick & Cooley, 2009)
- Municipal water (S California): 3 kWh/cubic meter (Gleick & Cooley, 2009)
- Seawater Desalination (reverse osmosis): 2.5 to 7 kWh/cubic meter (Gleick & Cooley, 2009)
- Seawater Desalination (reverse osmosis): 2 kWh/cubic meter (Elimelech & Phillip, 2011, p. S1)
- Bottled Water: 519 to 945 kWh/cubic meter [Gleick & Cooley, 2009; thermal energy units were converted to electrical energy units (3:1) to derive these values]

It was interesting to discover that AWGs used in tropical climates are competitive with bottled water. Keep in mind the apparently cheaper conventional sources may not even be available in some water scarce regions. The desalination costs do not include the apparently difficult to monetize costs of harming local ecosystems with brine disposal.

References:
Elimelch, M. & Phillip, W. A. (2011) Supporting Online Material for The Future of Seawater Desalination: Energy, Technology, and the Environment. Science 333, 712-717.
Gleick, P. H. & Cooley, H. S. (2009). Energy implications of bottled water. Environ. Res. Lett. 4 (2009) 014009 (6pp).
Young, R. (2014). Watts in a Drop of Water: Savings at the Water-Energy Nexus. An American Council for an Energy-Efficient Economy (ACEEE) White Paper. Retrieved from https://www.aceee.org/sites/default/files/watts-in-drops.pdf 

• Is there any air cleaning value to AWG? 

If the air entering the machine is strictly indoor air, the air filter in the machine may clean the air slightly but AWGs from credible suppliers are not intended to be air cleaners.

• COST: Do you have a unit cost for AWG on a per gallon basis?

From a typical retail price list, these are the USD unit costs per US gal of water production capacity when the air temperature is 85 F and the relative humidity is 75%:
- AWG rated for 5 gal/day: $300/gal (residential quality)
- AWG rated for 10 gal/day: $420/gal (balance of list is commercial/industrial quality)
- AWG rated for 40 gal/day: $178/gal
- AWG rated for 140 gal/day: $121/gal
- AWG rated for 800 gal/day: $98/gal
- AWG rated for 1800 gal/day: $82/gal

• What is the lifetime for the equipment?

Comparable equipment is used in air-conditioning. Typical equipment lifetimes range from 10 to 20 years given proper maintenance.

• What is the lifetime for an ultraviolet lamp?

12 months. The lamp must be changed annually even if it appears to be still working because the output may have decreased below the threshold for reliable inactivation of microbes.

• Over the 35 years you’ve been studying this sector, there has been a trail of broken dreams with few companies gaining long-term traction. How has the increased prevalence of these systems and recent funding news (like the $50M to Zero Mass Water [now called SOURCE Global]) changed the conversations you’re having? And, from what sectors or geographies are you hearing the greatest interest?

Conversations have not really changed. We are still firmly in the early to late majority phase (this terminology is from a 2018 article by Paul O’Callaghan and others). This stage lasts typically 12 to 16 years. I think this stage started about 2010. So, increased prevalence of systems and the SOURCE Global funding news are just part of this stage of the AWG industry. Sectors and geographies: Oddly, just in the past few days I have seen two references to US Military interest in AWGs. Otherwise, the drinking water supply sector in the United Arab Emirates is a bit of a hot spot for interest this year.
​

• Mojave Desert nighttime humidity is as high as 50% and daytime is much lower. It would seem as though the richest source of water is at night when the availability of sunlight is least. It would seem battery use is critical. How many kilowatts is required per 1000 gallons of water?

For air with a given water vapor content, the relative humidity value increases when temperature decreases (such as at night) and the relative humidity value decreases when temperature increases (with solar heating during the daytime). Water vapor content (the atmospheric water resource) actually is quite stable from day to night to next day being related to the properties of the air mass enveloping a region.  Modeling a chilled-coil AWG operating in the climate of Las Vegas shows that water production would be unreliable year-round with this type of machine. Therefore, a desiccant AWG should be considered. An AWG having a rotary solid-desiccant dehumidifier would produce water year-round (usually reasonably close to its water production specifications) according to an ASHRAE model. For an off-grid desiccant AWG, having battery power available during the night increases productivity of the system because the atmospheric water capture process can continue 24 hours per day. An off-grid desiccant AWG could use a solar thermal process during daylight hours to heat the desiccant to release water vapor for subsequent condensation into liquid water. Desiccant AWGs can also use an electric heater to reactivate the desiccant.

The energy cost of water produced by a desiccant AWG was estimated two ways (note that kilowatt is a unit of power---the energy unit is kilowatt x hours, kWh, which is power acting over a period of time):

a. Specifications for a line of industrial rotary desiccant dehumidifiers (using electrical energy) manufactured by Hangzhou Peritech Dehumidifying Equipment Co., Ltd. (http://www.desiccantwheeldehumidifier.com/sale-2082217-industrial-rotary-desiccant-dehumidifier-silica-gel-economical-dehumidifier.html). Their 14.4 L/day model produces water using 2.8 kWh/L (10.6 kWh/US gal or 10,600 kWh per 1000 US gal). Their 1,102 L/day model produces water using 1.3 kWh/L (4.9 kWh/US gal or 4,900 kWh per 1000 US gal).

b. Using information in the SOURCE Global (formerly Zero Mass Water) Patent Application US 2018/0043295 A1. The document includes an example of operation in Amman, Jordan at 14:00 on a July day. Airflow is 90 cfm. Relative humidity is 30%. A solar thermal panel with surface area 1.5 square meters provides 700 W (at 50% efficiency) to heat the desiccant to release captured water at the rate of 0.3 L/h. This information can be interpreted three different ways because international consensus is lacking on comparing different energy sources (e.g., solar thermal versus electricity; read more at the American Physical Society Site https://www.aps.org/policy/reports/popa-reports/energy/units.cfm). We need to make this comparison because the Peritech dehumidifiers and all chilled-coil AWGs are energized by electricity.
i. Thermal energy = electrical energy cost of water = (700 W x 1 h)/0.3 L = 2.33 kWh/L; efficiency of solar thermal assumed to be 100% as per OECD/IEA publication guidelines
ii. Equivalent electrical energy cost = 0.76 kWh/L; efficiency of solar thermal assumed to be 33% as per DOE/EIA (USA) publication guidelines
iii. Equivalent electrical energy cost = 1.17 kWh/L; efficiency of solar thermal assumed to be 50% as stated in the patent application

The range of energy costs for the SOURCE Global patent application example is 2.8 kWh/US gal (2,800 kWh per 1000 US gal) to 8.7 kWh/US gal (8,700 kWh per 1000 US gal).

Has widespread use of dehumidifiers and air-conditioners dripping condensate affected in the long-term the amount and geographical distribution of water vapour in the atmosphere? An analysis using data available from NOAA suggests not. The figure above shows the difference field of specific humidity resulting from subtracting the composite means (Jan to Dec) for the 30 year period 1951 to 1980 from the 39 year period 1981 to 2019, Several pools of higher specific humidity +2 g/kg are noticeable. These are likely related to climate change. Drying of about -2 g/kg is noticeable over the Sahara and Gobi deserts---more likely to be related to climate change than use of HVAC equipment. Overall, specific humidity has been remarkably stable (+/-1 g/kg) over the past seven decades.

Reference: NCEP Reanalysis Derived data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/   

Please join us for this webinar by registering at http://bit.ly/SGC-Oct20 where you will find additional information.

Here are some product design notes applicable to atmospheric water generator products. The notes are based on an interview with Mitch Maiman, Intelligent Product Solutions by William G. Wong of Electronic Design magazine (July 26, 2020).

Essential elements

• Objective market assessment (problem being solved for user, understanding of criteria inducing customer to buy)
• Define product requirements (features, functions, cost, and volumes)
• End product must deliver on a business opportunity

Common design mistakes to avoid

• Development activities lose sight of product requirements causing project to go off course and miss deadlines
• Over-designing for the application (increases cost, weight)---scheduling problems result
• Misunderstanding cost, time, and expertise required for the product design process
• Not enough reliability testing of the new product

Best process

• Tailor the design process to the project complexity, regulatory needs, and risk profile of the client

Embrace smart products

• Incorporate sensors, processing, and wireless communications (but avoid over-design)
• Smart product design usually needs a team with a wide range of expertise---mechanical, electrical, radio-frequency, embedded systems, and application software.

This quotation defines the fundamental market for the water-from-air industry.

"The pandemic has exposed huge inequalities in water security, with more than 2 billion people, half of schools, and one-quarter of health-care facilities lacking a basic water or sanitation service."---as stated by 16 co-signatories in Correspondence published in Nature 583, 360 (2020).

But, it is challenging to develop business models to address these markets in which the individual members seldom can afford innovations. Although technical water-from-air advancements remain important to work on, the need for business model inventiveness is likely to be even more necessary.  

Journalist Verity Ratcliffe of Bloomberg wrote an interesting article about Zero Mass Water's installation supplying water-from-air to a bottled water plant in Dubai, UAE.

For technical details, see this page: ​https://www.atmoswater.com/case-studies-zero-mass-water-inc.html

This is an interesting article about the drinking-water-from-air industry. It also includes a section on fog harvesting. Atmoswater Research got a nice mention!

Water-from-air systems often use ultraviolet light means to sanitize the incoming air, the stored water, and the water as it is being dispensed. This 4-page fact sheet, by the nonprofit IUVA, is useful knowledge for the water-from-air industry community as it copes with the COVID-19 pandemic.

Recently, I was invited to discuss some aspects of water-from-air technologies as posts (each about a one minute read) in the GWW Connect Network. I posted the seventh and final article today. Here are links to the posts.

1. Significant Milestones
2. Crucial success factors for companies to remain viable in the water-from-air market
3. Where do I see the most impact from water-from-air technology solutions?
4. What should investors know before investing in the water-from-air industry?
5. What should users of water-from-air systems know about implementation and maintenance?
6. What type of training do I recommend for someone interested in entering this field?
7. What are my favourite breakthroughs in the water-from-air field?

This article is a good overview of the COVID-19 virus in relation to systems processing drinking water and wastewater. Water-from-air machines (atmospheric water generators, AWGs) are, of course, small-scale drinking water systems. Even though the drinking water within the system may be safe, spigot handles and machine surfaces could be contaminated by viruses and bacteria. Machine users should wash their hands before operating the machine. Machine surfaces, spigots, and spigot handles should be sanitized frequently.

For the air-side of water-from-air systems, relevant information is provided at ASHRAE Resources Available to Address COVID-19 Concerns. 

For the water-side of water-from-air systems there are two good sources of information:

1. The World Health Organization (WHO) Technical Brief titled, Water, sanitation, hygiene and waste management for COVID-19. 
2. Water Quality Association Coronavirus (COVID-19) Update 

This newly published article, by water industry experts Mary Conley Eggert and Graham Symmonds, is worthwhile reading for current perspectives about the role of water-from-air technologies in drinking water supply infrastructures.

The Water-from-Air Industry is actively growing! This chart is from the data table below tabulating the founding years for Water-from-Air companies [suppliers of Atmospheric Water Generators (AWGs)]. Companies that failed between 1990 and the present are not included. Only those companies with active websites as of today are included. Founding year information is from the company websites or the LinkedIn profiles of the companies or their founders. The two pre-1990 companies were not set up initially as water-from-air equipment suppliers. Companies started in the 2016–2017 peak years were not apparently a direct response to the Water Abundance XPrize competition which ran during 2016–2018. Founding years were not available for 11 of the 73 companies listed below. The last 10 years saw the formation of 37 firms—half of the existing companies. There has been no apparent merger and acquisition activity. Dozens of companies are marketing actively their AWGs. At least two or three dozen units are operating worldwide (see Case Studies page). According to O'Callaghan and others (2018) when "at least 3 companies actively offer versions of the technology; [with] more than 12 full-scale units in operation" this is one signal the industry is in the "Early and Late Majority" stage which can typically last 12 to 16 years. Two other signals stated by O'Callaghan and colleagues are that "Consulting engineers now specify the technology..." and "Efficiencies [are] gained in engineering design and process optimization." 

Reference: O'Callaghan, P. and others (2018). Development and Application of a Model to Study Water Technology Adoption. Water Environment Research, June 2018, 563–574.

pre-1990 (2)

• Francopost Srl, Italy (1961)
• Yildiz Makina Sanayi Ltd., Turkey (1983)

1991
1992 (1)

• Yueqing Kemao Electric Co., Ltd, China

1993
1994
1995
1996
1997 (2)

• Atmoswater Research
• Excel Water Technology, Inc., Virginia, USA

1998 (2)

• Shenzhen FND Air & Water Technology Development Co., Ltd., China
• Water Technologies International, Inc., Florida, USA 

1999
2000
2001 (2)

• Hendrx, China
• MSP Technology.com, LLC, Kentucky, USA

2002 (1)

• Island Sky Corporation, Florida, USA

2003 (4)

• Air2Water LLC, California, USA
• Aqua Sciences, Inc., Florida, USA
• Atlantis Solar and Wind LLC, California, USA
• Canadian Dew Technologies Inc., British Columbia, Canada​ 

2004 (4)

• Aquaer Generators S.L., Spain
• Global Site Solutions Inc., British Columbia, Canada
• Ray Agua Universal, Spain
• WaterMaker (India) Pvt. Ltd., India

2005
2006 (2)

• Air Solar Water & Rain Capture, Washington, USA
• Air Water™, South Africa 

2007 (1)

• EuroSport Active World Corp (EAWC) Technologies, Florida, USA

2008 (3)

• Genaq Technologies S. L., Spain
• Quest Water Solutions, Inc,, British Columbia, Canada
• Rainmaker Worldwide Inc., Ontario, Canada

2009 (1)

• Veragon Srl, Italy

2010 (4)

• AT Company, Korea
• AtmoWater Inc. (Ser-Manukyan Family Holdings), USA
• DewPoint Systems, Hawaii, USA
• ​SEAS SA, Switzerland
• Water-gen LTD, Israel

2011 (2)

• Atmospheric Water Solutions, Florida, USA
• Infinite Water, Inc., New York, USA

2012 (3)

• Drinkable Air, Inc., Florida, USA​
• SunToWater Technologies, LLC, Texas, USA
• World Environmental Solutions Pty Limited, Australia

2013 (2)

• Aquavolve, LLC, Massachusetts, USA
• Vitality Vector, BV, Netherlands​

2014 (4)

• Atmospheric Water Generator, LLC (Quench Innovations), Florida, USA
• AWG Contracting, LLC, Texas, USA
• Skywell Solutions Ltd (Requench), UK
• Zero Mass Water, Inc., Arizona, USA

2015 (4)

• FreshWater Solutions, Chile
• PanLbilt Global, Illinois, USA
• Water From Air, South Africa
• Water Generating Systems, LLC, Washington, DC, USA

2016 (6)

• Akash Ganga (Clean Water Generator Pvt. Ltd.), India
• Amigoz Innovative Technologies Pvt. Ltd (Aguaer), India
• Aquacello, South Africa
• Generation Water Company Limited, Singapore
• Maithri Aquatech Pvt Limited, India
• Skysource.org, California, USA

2017 (8)

• Akvo Atmospheric Water Systems Pvt. Ltd., India
• Drupps AB, Sweden
• Jordan's Air 2 Water, Minnesota, USA​​
• Majik Water, Kenya
• Talisa Water, South Africa
• Tsunami Products, Inc., Washington, USA
• Uravu Labs, India
• Watergen USA, Florida, USA

2018 (2)

• Innovative Teknologies, India
• LiquidSky, India

2019 (1)

• Agua de Sol, France

Unknown year (11)

• Aid Water Global, LLC, Texas, USA
• Air 2 Water Solutions, California, USA
• Air-O-Water, India
• Airwaterex Ltd, Cyprus​
• Ardor Marketing Pte Ltd, Singapore
• AW International Ltd, Puerto Rico
• GOODWATER Beteiligungs GmbH, Austria
• Proficient Machine and Automation, Michigan, USA
• RainInABox.org (Rocillo Innovative Technologies, Inc.), California, USA
• Skywell, LLC, California, USA
• Water World Solution, France

This YouTube video by the Dutch foundation, Happy With Water Foundation, reviews several atmospheric water vapour processing methods and then states that an absorption cooling method using solar energy and vacuum tubes with heat pipes reduces the energy cost of water making it relatively more affordable and practical compared to most other options.

For some time I have wanted to highlight this interesting water-from-air system. The photo shows a prototype system using glycerol as the liquid desiccant to absorb water vapour from the air on Sal Island in the eastern tropical Atlantic Ocean (17°N, 23°W). The prototype was designed and built by Dr. Pavel Lehky who holds United States Patent 9,200,434 B2 for the system. The field trials were done during Team AKVOS's participation in the Water Abundance XPRIZE competition. I was a member of the team. During a typical night at the site, the absorption module with its 9 square metres of surface area absorbed over 4 L of water. The 0.25 sq. m. production module was able to recover about 0.3 L of this during a typical day. So, one of the lessons from the trial was the water production module area has to be better matched to the capacity of the absorption module. Improving the efficiency of the water production module is also of benefit—this is a focus of ongoing design improvements. Find out more about Stiftung Sanakvo (Team AKVOS) at their website. Sanakvo also has a video on YouTube with an explanation of the system and showing the prototype operating during the field trial.

Visit the new Case Studies page to learn about practical applications of water-from-air systems!

Drinking-water Industry Organizations Links is a new page on the Atmoswater Research website. I hope people in the industry find it to be useful. Please tell me if there are other industry organizations that should be listed on this page. Thanks!

Do atmospheric water generators—producing water with low total dissolved solids (TDS)—need to incorporate a mineralization feature into their design? Reading this article by the Water Quality Association gives you the knowledge to make an informed choice or to have a useful discussion about this topic.

The Water Quality Association has a useful knowledge-base, much of it relevant to water-from-air systems, available on its Technical Fact Sheets page.

Patricia Oliver, a librarian in St. Croix, phoned me. Her library used an atmospheric water generator (AWG) and it worked very well year-round---climate conditions are ideal for operating water-from-air systems. Ms Oliver believes AWGs are much needed in St. Croix. The problem is that local firms are wary of importing machines because there are limited options for servicing the machines. If you, as a water-from-air systems supplier, would like to enter into a dialog with Ms Oliver about contributing to solutions for the drinking water supply challenges in St. Croix, please ask me for her contact details. Thank you!

The University of California, Berkley research group led by Omar M. Yaghi published recently an article in ACS Central Science describing how they built and tested a metal-organic framework water harvester prototype. The system produced fresh water at the rate of 0.7 L/day in the Mojave Desert during a 3-day trial (October 17–20, 2018). During this period the ambient air dew-point was less than 5 °C for 85% of the time. 

You can read the update by Jeff Szur at this link: ​https://mailchi.mp/5b1d9c7272fb/my-new-venture?fbclid=IwAR3ZLsQGIUKDRT3lPfATLn4ATO2Shjfjs1QKXEus_9L5rZRl2N1cUL0FBt0

​"Thanks Roland, I have great admiration for your website and content, a great resource!"
- comment from a new LinkedIn connection today

Are you a supplier of products to the water-from-air industry? Attract more traffic to your website and gain new sales prospects by advertising on our Suppliers Links page. This is the most visited page on our site with visitors from around the world. Faced with the list of 70 or so suppliers, people looking for water-from-air systems are a bit perplexed as to where to start their search for a reliable equipment source. It is easy to imagine they start by looking at who is advertising—advertisers have enhanced credibility.

The Atmoswater Research website requires money and time to maintain and improve the content for the benefit of the entire industry. Advertising with us and purchasing our digital goods helps provide the financial support needed for long term evolution. A big thank you to our customers!

Please contact Roland Wahlgren to discuss your company's plans for advertising on our site!

Recently, the magazine, Inc., published an article about the Source Hydropanel manufactured by Zero Mass Water. A sidebar in the article said the device produces 5 litres per day of clean water and that the cost for each panel is USD 2000. A link to the article was posted on LinkedIn. A LinkedIn member wondered what would be the "levelized" cost of water per gallon. This blog post shows one method for answering the question. The spreadsheet shows that direct capital cost is only part of the equation. But, for a quick analysis let us proceed with the bare bones information in the Inc. article.

For a 10 year equipment lifetime, cost of water (USD) is $0.41 per gallon. For 15 years it is $0.28 per gallon and for 20 years it is $0.21 per gallon. 

Today, I learned about Aalto University's Water Scarcity Atlas from The Water Network. The atlas is a useful and credible resource for learning about various aspects of the water supply challenges facing humanity. For those of us in the water-from-air community it is definitely worth visiting and bookmarking. The atlas is a useful guide to the regions on which to focus water-from-air research and development efforts.The data & code section of the atlas website had a link to the City Water Map Initiative whose data source was

McDonald and others (2014). Water on an urban planet: Urbanization and the reach of urban water infrastructure. Global Environmental Change 27, 96–105.

This paper gives the results of the first global survey of the water sources for the world's largest cities. Table 2 in the paper lists the largest cities enduring water stress. The cities (in order of population) are Tokyo, Delhi, Mexico City, Shanghai, Beijing, Kolkata, Karachi, Los Angeles, Rio de Janeiro, Moscow, Istanbul, Shenzhen, Chongqing, Lima, London (UK), Wuhan, Tianjin, Chennai, Bengaluru, and Hyderabad.