Atmospheric water generator DIY: what you can build, and what you cannot

The build is not the hard part

A dehumidifier already does the whole extraction job. It pulls room air across a cold coil, water condenses, and it drips into a bucket. That is an atmospheric water generator with no marketing attached. A commercial unit adds three things: a food grade path for the water instead of a plastic bin, disinfection that runs continuously, and a filter stack on the way out.

So the honest question for a home build is not "can I collect the water", because you can, today, for the price of a dehumidifier. It is "can I make that water safe, and keep it safe in the tank".

What the EPA found, and why it matters to your bucket

The EPA ran a commercial atmospheric water generator continuously for three months and published the results in November 2019. On the chemistry the machine did well: nothing measured above the primary or secondary drinking water standards, and no Legionella, mycobacteria, fecal coliforms or E. coli were detected.

The catch was biology. Heterotrophic plate counts were high in the raw water and stayed high after the machine's own treatment. The brief's recommendation is the sentence to copy into any home build: bacterial growth "could be addressed by incorporating chlorination or ozonation as an additional disinfection process", and by keeping a disinfectant residual in the storage.

There is a reason water from air behaves this way. It comes out close to distilled, with almost no minerals in it, which means nothing in the water discourages anything from growing, and the water itself is aggressive toward metal. Distilled and clean are not the same word.

EPA, Atmospheric Water Generation Technology, EPA/600/F-19/129, November 2019. That study used a commercial unit with its own filtration; a bucket under a dehumidifier has none of it.

The separate problem of the coil

Water that condenses on an air conditioner coil is the same physics and a worse starting point. In EPA sampling of condensate from building air handling units, heterotrophic counts ran in the thousands to tens of thousands of colonies per millilitre, culturable Legionella was found including L. pneumophila serogroup 1, and one site showed elevated lead and copper leaching from old plumbing. The drain pan biofilm was consistently dirtier than the water itself.

That is why every US code that mentions captured condensate puts it in the non potable column. The 2021 International Plumbing Code lists it as an alternate on site non potable water source, and Texas rules for alternative on site water allow condensate for irrigation and for flushing, not for drinking.

We wrote the longer version of that question in is water from your air conditioner safe to drink.

EPA Science Inventory, water quality of air conditioning condensate, presentations of 20 September 2022 and March 2023. 2021 International Plumbing Code, chapter 13. Texas Administrative Code, title 30, sections 210.81 to 210.85.

What a home build actually needs, in order

1. A clean collection path. Food grade tubing and a food grade tank. Not a garage bucket, not vinyl hose sold for garden use.
2. Particle filtration first. Dust from the room ends up in the water, and it feeds everything downstream.
3. Disinfection that keeps running. Ultraviolet at the tap kills what passes through it and does nothing for the tank behind it. A residual, chlorine or ozone, is what protects standing water. This is the step most builds skip.
4. Carbon after disinfection. Volatile organic compounds in room air dissolve into the condensate, and they are also the carbon that feeds bacterial growth.
5. Remineralisation. For taste, and to stop the water from attacking your own plumbing and fittings.
6. A test, not a feeling. A home total coliform test costs a few dollars. Nothing above tells you the build worked; the test does.

There is a published standard for the manufactured version of this, ASSE 1090-2020, and it requires filtration and disinfection controls as part of the device. A home build has no certifier. That does not make it impossible. It makes the test the only honest evidence you will have.

The electricity bill decides more than the build

Extraction costs energy, and the energy does not care whether the box was built in a factory or a garage. Manufacturers publish 240 to 400 watt hours per litre in their rating conditions. The one long field measurement we could find, a commercial unit run for a year in a hot humid climate and published on 1 November 2022, averaged 2.25 kilowatt hours per litre.

At the US residential average of 18.34 cents per kilowatt hour, which is the EIA figure for June 2026 published on 26 August 2026, a gallon costs 28 cents at the brochure figure and 1 dollar 56 at the measured one. A dehumidifier in a cool dry room lands on the bad end of that range, because it runs long and catches little.

We worked the whole arithmetic out, including what it means per day for a 20 litre unit, in what a gallon from a water from air machine actually costs.

Where a build makes sense, and where it does not

It makes sense as a second source in warm humid air, with grid power, when the water you have is unreliable rather than absent. It is a poor outage plan, because the machine stops exactly when the power does, and a poor desert plan, because the air you are trying to squeeze is the driest air in the country.

If you have a roof and rain, the comparison is not close. Our rain barrel calculator gives the gallons your roof catches per inch, using NOAA state normals, and the barrel keeps working through a blackout.

Sources, with the date of each

• EPA, Atmospheric Water Generation Technology, EPA/600/F-19/129, November 2019.
• EPA Science Inventory, water quality of air conditioning condensate, presentations of 20 September 2022 and March 2023, and the HVAC condensate reuse work of 2018.
• 2021 International Plumbing Code, chapter 13, non potable water systems. Texas Administrative Code, title 30, sections 210.81 to 210.85.
• Ahmad and others, twelve months of a commercial unit in Sharjah, Case Studies in Chemical and Environmental Engineering, published 1 November 2022.
• U.S. Energy Information Administration, Electric Power Monthly, Table 5.3, data for June 2026, published 26 August 2026.
• ASSE 1090-2020, Performance Requirements for Drinking Water Atmospheric Water Generators.

We did not state, because we could not confirm: the current status of the NSF P343 protocol, and the widely repeated claim that real output is 40 to 70 per cent of the rating, which we found only on commercial blogs.