Can HVAC Condensate Be Put to Work in Gardens and Showers?

In places where fresh water is costly, or in short supply, heat pumps and air conditioners already offer a small but steady source of H20. Why waste it?

You may have heard about devices that can pull water out of thin air, from companies such as Watergen, (based in Israel). They have a mobile, 12 volt product that weighs 66 lbs., and will produce about 5.5 gallons of water over 24 hours. It runs on 380 watts, so requires about 9.12 kilowatts to produce that much H20. It has plastic fins, not metal ones like most compressors, and is supposed to work in dry climates with 20 percent humidity.

Double duty. My heat pump compressor delivers a regular trickle of condensate water to a small raised bed garden.

For water “extraction” from air on a much larger scale, a U.S. company called Genesis has developed the WaterCube. It weighs 600 lbs., and will produce 120 gallons of purified water a day from the surrounding air. The process, however, requires substantial energy. At 80 degrees ambient temperature, with 60% relative humidity, it uses 6000 watts of power to do this. 

Over 24 hours, that’s 144 kilowatts per day. If you tried to power the unit with solar panels, you would need 72 panels at 400 watts each, (assuming an average of 5 peak sunlight hours per day). That’s far more than almost any residential property can sustain.

Both of these dedicated water makers include purification, an important feature, so you know you’re getting potable quality H20 at all times. But what about water extractors that we already have installed in our homes? Are we missing a “free” source of water collection?

An Overlooked Water “Extractor?”

Let’s look at some devices that incidentally pull moisture out of thin air through condensation on evaporator coils: residential heat pumps and air conditioners. By way of reference, I have a SEER2 22, 12,000 Btu heat pump that coincidentally uses about 380 watts (in cooling mode). At 90 percent humidity, in 80 degrees or so, over 24 hours, I would expect it to produce 5-10 gallons of condensation water. 

In a pinch, could I drink this stuff safely? What about using it to run laundry or water plants. It turns out I’m not the first to ask.

A handful of studies have examined the possibility of re-using condensate water from heat pumps, along with air conditioners. Their results are encouraging. 

“Attained water has to some extent basic pH, close to neutral range. Total dissolved solids, copper, lead, total hardness, electrical conductivity, and alkalinity of condensed water are in very short ranges. On average, every 2-ton air conditioner formed 25 liters of water each day. This research shows the feasibility study of using this condensed water in the battery, automobile radiator, boiler, toilet flushing and washing clothes.” Source

This is encouraging. A different report came up with similar findings. “The condensate that collects on HVAC units amounts to a significant volume, and could potentially serve as an alternate water source. Moreover, its quality is relatively high as the water is almost mineral free, and has a very low content of Total Dissolved Solids (TDS) and low conductivity. With regard to water sustainability, collection of condensate from air conditioning systems has tremendous potential because it is an inherent byproduct of HVAC units.”

I should add, as a caveat, that every heat pump or air conditioner is a little different, depending on where and how it’s manufactured. And if you’re borrowing water from condensate, you want to make sure it’s clean and well maintained. I can’t guarantee that your model is dripping  pure water. You’d need to test it to make sure. 

The Potable Purity Question

A Jordanian study took a deep dive into the prospect of using air conditioning condensate as a potable resource. They found, through numerous tests, that the water fell well within that country’s safe drinking water parameters. 

“The laboratory testing and data analysis of the obtained 120 samples of condensate water revealed an exceptional water quality level that meets both Jordanian drinking water standards and the Food and Agriculture Organisation (FAO) irrigation water guidelines.

The same study estimates the approximate daily output of water from a residential sized air conditioner:

“The water production of modern air conditioners ranges from 15 to 70 L per day (4 to 18 gallons), depending on the capacity of the unit. As an illustration, a 2000-pound air conditioner operating for 7–8 hours has the potential to produce approximately 10 L (2.6 gallons) of water.”

Field Test in Process

I decided to do a little experiment with my latest installed mini split. I ran the drainage from both the head and the compressor into a perforated pipe. That way, I can capture condensation from both heating and cooling modes. I then submerged a perforated pipe in a raised garden bed.

So far, the system is performing nicely, keeping the soil in the bed moist for several weeks, despite some dry weather here in the Southeast winter, operating at the same cost as a dedicated atmospheric water extractor, but doing double duty—cooling the house at the same time it waters plants. I am in the process of having the condensate tested by the local university, and will post my results here when I get them.

I have noticed that the amount of condensate varies dramatically with the relative humidity. That’s one of the limitations of this water-collection-as-a-byproduct of heating or cooling. If you were depending on it for survival, you might look at one of the dedicated water extractors I mentioned above. But since I’m already heating and cooling, why not do double duty with the electricity I’m using?

And by the way, my heat pumps are solar-hybrid, so part of the day, they run on nothing but sunlight.