My question is about using condensed water from air conditioners. Can this water be treated with reverse osmosis plants and ultraviolet so you can use it? How pure will this water be? If this water can be used for bathing, washing clothes, washing cars, etc... then we can save more land water currents!

And can we drink it? Some threads I found say it is not safe to drink but what happens and how pure will it be after reverse osmosis?

  • Many new energy efficient window-unit models use a slinger fan to splash the condensed water up on the hot condenser coils to improve efficiency (and to get rid of the water). If you drain this water away for other uses, you'll be reducing the energy efficiency of the unit and using even more electricity in purifying the water.
    – Johnny
    Feb 11 '15 at 7:08
  • I was thinking of this idea for a sailboat or a campervan. To keep from hauling around a lot of heavy water that takes up a lot of space, just make it from your air conditioner and keep cool at the same time. I have been searching the Internet for the last half of the day looking for answers, like distilling the water, ... no luck. It's like someone does not want you to find the answer.
    – user9070
    Oct 27 '20 at 22:44

There are some issues with this:

  1. Internally the drip catcher tray is exposed to the air currents running through the compressor. As such, it will have dust, pollen, and general crud -- Pretty much what you find on your swiffer.

  2. Sometimes these catch trays are designed cheaply, so the water doesn't drain until it gets to be 1/8 to 3/4" deep. So you have dirt soup. All kinds of stuff find this a happy place to live. (Wasn't Legionnaires Disease traced to mold in water in an air conditioner?) This damp tray of stuff is responsible for some of the odd smells that come out of an air conditioner.

Overall I would prefer to drink from a fresh mud puddle.

Could you run it through reverse osmosis? Yes. I'd want to run it through a good filter first to get out the crud. Indeed: If you know that there is nothing toxic on the tray liner (galvanized steel say) then filtering may be enough before UV treatment.

Also: The amount of water isn't huge. Not having lived with an air conditioner, I can't say for sure, but I'd be surprised it it were more than a few gallons a day. This is too much work to salvage a couple of toilet flushes a day in the cooling season. Direct the drain hose to your favorite tree.

For water conservation, you have much better targets:

  • Grey water -- everything but the toilet and kitchen sink/dishwasher drain. This water is unfit to drink, and contains soap and dirt. Neither of these harm plants. It is quite reasonable to internally divert this, and either drop into a cistern that you use for watering in your yard, or run to a tiny wetland where it can soak into the earth.

Note that this process is trickier in climates where you have extended periods of frozen ground.

Addendum in response to comment:

For years I had a neighbour who, to save water costs diverted his washing machine through a 6 foot pipe to a pond which he then used for watering his garden. No problems were seen around the pond and I can testify that the garden produced wizard squash.

Observations of culverts where there is splashing on the water hitting the pond below: There are lots of natural soaps. 2-3 inches of foam below a culvert draining land that hadn't had a chemical sprayed on them in 10 years...

  • No, Legionella has no link with molds, it's a bacterial issue.
    – user2451
    May 17 '16 at 8:34
  • "Neither of these harm plants." - I'm not sure about this. Soap is basic so it'll make the soil more basic as well, which may be bad for plants. There may be other things in your toiletries that aren't good for plants, e.g. zinc pyrithione in your shampoo, silicones in your conditioner, synthetic fragrances in just about everything, etc. My understanding is that graywater is best used to flush toilets with.
    – kitkat
    Oct 28 '20 at 21:19

Another angle to it is to see if the condensate quantity can be reduced. While some is expected to lower the humidity level, some operating conditions (low temperature setting with low fan speed) promote additional condensation. In effect, drawing outside humidity in and then discharging the cold condensate. This is quite frequent when a cooling unit is set to both low temperature and low fan, increasing the condensate quantity.

The saving in energy from proper operation outweigh the value of water.

At the other extreme end, some condensers are sold on the market to supply water for remote construction sites. Coastal deserts in the middle east are very humid in the morning making.

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