Building a (mostly) Self-contained Condensate Recycler.





Introduction: Building a (mostly) Self-contained Condensate Recycler.

Here in Tucson, AZ, air conditioning is so vital that if you're renting, your landlord has to provide it by law. The relief is almost worth the high electric bills that come in the summer months, but one thing has always bugged me.

If you have a cooler, whether it's a compressor/condenser style or an evaporative, or swamp cooler, there is always going to be some waste water involved. During the 100+ season, this is especially true, and it can create problems like unwanted weed growth around your machine and possibly damage to your foundation. In addition, the tap water here is piped in from remote locations and it's finite. Waste is dumb when you can prevent it easily, so I looked around for materials to create a solution.

Step 1: Gathering the Parts

I took a peek around the garage, and noticed I had what I needed. Your mileage may vary, of course. Scouring secondhand shops, yard sales, and classifieds should yield the parts without too much trouble.

I didn't take photos of the assembly process, because to be honest I was winging it and wasn't sure it would work. Here instead is a shot with the parts explained.

You'll need:

1. An aquarium or reptile tank. Mine's about 10 gallons. I picked one with a screen top to prevent mosquito breeding. You could probably adapt the design to a hooded tank, though.

2. A low volume fountain pump. This one still has the fountain attached, but you could hook tubing to a bare one and install it in any kind of fixure you could think of. If you are just using an aquarium, you might be able to use the existing filter system and hack it to add an output.

3. Heavy duty duct tape.

4. Access to a file or rotary tool.

5. An outdoor source of electricity.

Step 2: Putting It Together

Hopefully it's pretty straightforward from the picture, but I'm happy to explain.

1. Find your condensate output. On an a/c unit, there will be a pipe coming from the house, usually near the compressor unit. On a swamp cooler, there will usually be a length of tubing. Position your tank so that it can receive the drip most effectively. The condensate will leak into the tank, slowly but quite surely. After a day or so, the tank will be nearly full. It's time to put that water to use.

2. Remove your screen, submerge the pump and make sure the output tube fits securely. Many of these have suction cups which will be helpful. Note that running a pump dry will damage it.

3. Modify the screen.

If you have a sliding screen use a file or rotary tool to carve out a pair of divots for the pump's power cord and the output tubing. I found that it produced a better fit, but didn't carve enough to prevent the tank from being useful in its original purpose. If you have a screen that clamps on, you could use pliers to give the power cord and tube somewhere to sit.

4. Position the pump so that it will flow back into your tank. In my case I found an easy hanging spot on the gas meter, and will probably secure it with wire.

5. Seal any gap between the screen and tank with duct tape. I prefer Gorilla tape because it has a longer life span outside.

You're done. Plug in your pump and you have a recycling fountain. Interrupt the flow with a bottle, and you have an easy way to water your plants.

Step 3: Good on You, You Just Saved Some Water From Oblivion (but Be Careful With It)

I'm using mine to water potted aloe plants, because let's face it, you can get a lot of little burns and cuts when you're figuring things out. I have also considered some kind of drip system for the plants that will eventually live in the tire garden I just started building, but that will require further experimentation. Naturally I want to look into rainwater harvesting as well because this only works on a small scale, but in the meantime I can re-use the water my cooler was dumping into the abyss and feel a little less guilty about having it on in the first place.

Please note: I do not intend to use this water for drinking, and I don't recommend you do it either.


For the curious, I just called a local HVAC shop and asked about the toxicity of condensate. I was told that it should be fine, because it's just water vapor collected from the air, a by-product of the cooling process and not involved at all with the freon. They said it was fine to use for watering plants.

Since then, I've been notified via comments that it's not the water I should worry about, but the path it takes to the collector. In my case, it's an old pvc pipe which has seen better days. In the collector, the water is exposed to air and sun, so it's essentially a bacteria farm. I've been warned about Legionnaire's Disease, and I'm sure it's not the only bug that could be growing in this water. Until I know for sure, I will be using this water only for decorative plants and not for veggies.

In the meantime, I've decided to simply divert the condensate, via pvc parts, into a homemade planter built from a used tire. I've transplanted aloe plants into fresh soil and I'll be monitoring them to see how they respond to the condensate. At least this way something's getting watered, the water doesn't go straight to my foundation, etc. One experiment begets another.

Thanks to everyone who's been giving me feedback and suggestions.



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    I collect air conditioner condensate year round. In July and August I can fill a 55g drum in about 30 days from condensate alone. I use that to water the flowers around my property.

    All these comments were very interesting to me. Two years ago, I decided to add a piece of PVC pipe to the end of my AC condensate drain pipe, so that the water would travel further from foundation. Then, to shade AC from Florida sun, decided to plant what gets called Mexican sunflower around here ... had collected the seeds from dried flowers the prior fall.

    Figured the condensate water would keep it well irrigated without me needing to think about it at all (I run my AC almost year-round, as I'm heat and humidity sensitive). I've had to cut the shrub back several times, as it grows and flowers up a storm ... last time, it got higher than roof before I fully realized it, and then a bad wind and thunder storm half-uprooted the plant.

    So, I cut it all back to a few feet high, added some soil around the base, and ignored it. Several months later, the thing is thriving, in bloom yet again, and will need trimming by spring. The only direct water is from the AC condensate line (and occasional rain).

    But would I even think of using this water for anything else? Not a chance!

    I've seen some comments here and on other posts about Legionnaires' disease and thought I could contribute some information from a little, basic research.

    Foremost, I don't pretend to be otherwise knowledgable about this topic except for the few hours I have spent reading Wikipedia articles, the CDC page about Legionella bacteria, and some other general internet searching. But, I think the info I have found can be helpful.

    Wikipedia: Legionellosis

    Wikipedia: Legionella pneumophila

    CDC: Patient Facts, Legionella

    Simple Facts

    1) Legionella bacteria are (a) aquatic and (b) aerobic. So, they mostly form in water and can grow anywhere there is oxygen: water and air, for example.

    2) Following that, infection occurs from breathing in the bacteria from a vapor or mist. Evaporated water from contaminated sources is the concern here, hence the issue about condensate from an HVAC system.

    3) Most people exposed to Legionella are not infected. But if you do come down with an infection, it is serious and can be fatal. The symptoms are very much like that of pneumonia.

    4) The bacteria are not spread from one person to another.

    5) Legionella can also be found in amoebae in soil, compost, and potting mixes.


    I think it's common sense that we are talking about two possible ways of Legionella being a problem in your garden. On one hand, we worry about it getting into the produce. On the other, as the above facts point out, we should also worry about the water, and the air around the water, that we are using from the HVAC system.

    To address the first case, take a look at the range of temperatures affecting Legionella; this is available in the Wikipedia article. Compare these to common cooking temperatures.

    If you are pairing veggies with meat, you will likely kill any bacteria including Legionella pneumophila. If you are steaming veggies, you almost certainly kill them considering it takes 212-F or 100-C to boil water; I'd assume the residual steam is similarly hot, though I don't actually know. Along the same line, if you are making soup or otherwise boiling the veggies for even just a few minutes, you will definitely kill the bacteria. I can't recall a soup recipe that doesn't call for bringing it to a boil and then simmering for at least 30 minutes. Anything above 151-F or 66-C will kill the bacteria within minutes. And 70-C or 158-F would lead to absolute disinfection.

    On that note, though, I'm not real sure that plants would even sustain the bacteria. There was no mention of such instances in anything I read, which was much more than the above cited pages to be clear. Being aquatic, the bacteria "live" in water; being aerobic, they grow where there is oxygen. Aside from being "infected," the plant could not otherwise play the part of a reservoir or host for the bacteria.

    Furthermore, I don't believe that the plants become "infected" as one of the most common hosts for Legionella pneumophila is an amoeba found in soil: Acanthamoeba castellanii. That's right, soil! In fact, it's possible that the bacteria are in soil, compost, and even potting mixes and can be kicked up into the air with dust, where you can breathe in the bacteria. We all garden with much of this, so I figure (1) the CDC must be correct when they say most people that are exposed are not infected and (2) it sure doesn't seem to be affecting plants.

    The only concern that I can see remaining is with regards to the vapors from this possibly contaminated water as it evaporates from your garden, as opposed to being taken up by the plants.

    FACT: this water, before being used for irrigation, is already being evaporated into the air around you -- the HVAC condensate outlet is already disposing of the water. Some seeps into soil (is it affecting your grass?) and some will no doubt evaporate (is that affecting you?)

    Legionella have been shown to have an effect in communities and up to several miles away. If you don't already have an outbreak in your area, and I'm sure you would know about it, then it's probably just as safe to let that water evaporate from your garden as it is to let it evaporate from the ground around the condensate outlet.

    It's not likely in your produce, but if you think it is, common sense guidelines for preparing food should take care of that.

    It's not likely a problem evaporating from the water source because if it were, you wouldn't be reading this; you'd already be in the hospital with Legionellosis.

    If an outbreak of Legionellosis should occur in your area, then go to back to plain old manual watering until all seems well again. Otherwise, I'm sure it's fine. I feel compelled here to reiterate that I'm no expert. 

    Interesting Instructable! I have a question. Could the water be recycled by using it to help cool the smaller and hotter of the two freon lines that run between the condenser and evaporator? A container similar to a small gutter could be put around a short length of the pipe and the condensate water could drain into that container. The pipe is very hot and would surely completely evaporate the water in the container quite easily. My house has a crawl space where these pipes run so a container up to around 8 or 10 feet would be no problem at all to install. Even a piece of split PVC pipe could be used. The condenser water could help cool the pipe and the freon it is carrying thereby increasing the effeciency of the AC unit. Even a little cooling could help save some money.

    I've been an UA, Local 250 Union HVAC&R; Service technician for 20 years, and you are right that it would make scene to cool the hotter line coming from the condenser outside, however Air conditioning systems work on the Pressure Temperature relationship, Cooling the hotter line is called sub-cooling and does make a systems effeciency go up, WAY WAY up. and if you whir to over cool the line too much your indoor coil would make only ICE, blocking the air flow and costing you lots of money in loss of effeciency. SO if we throw the T&P; out of whack by over cooling the line, OR like I've seen many times on residential calls people hook up water hoses to spray water on the condenser outside, all that happens is you cost your self more money on your electric bill. The best thing to do is have your A/C unit serviced by an honest company, change your filter when you should and keep the whole system clean, that will save you the most money. Or better yet just turn it off, A/C is a luxury and not a necessity. And YES I work in PALM SPRINGS So Cal, where it gets 121 in the summer, if I can work out in the heat, you can sit in your home without A/C. ;P

    godfish thanks for the info! I was just getting ready to mist my condenser with rain barrel water....

    godfish: Thanks for the information. I suppose it would be nearly impossible to determine if the 5 to 10 gallons of condensate water would cool the hot tubing too much so I guess this idea could help but is not very practical since the effect could over do it and actually cause problems. However, I am surprised by the fact that cooling the outdoor unit with a water hose can cause the indoor unit to freeze up, but I guess it does make sense now that you mention it. One more thing - I have to disagree with you on AC not being necessary. I know there was a time not to long ago when nobody had AC but as for me - I could not live here in South Texas without it. LOL No, seriously - considering how many seniors die every year from the extreme heat, I would think it safe to say that AC can even prolong some people's lives. I plan to make it well beyond 100 with the help of AC. I want to thank you again you for your professional opinion. That is the nice thing about this site. We backyard do-it-ourselfers can get advice and help from experienced professional like yourself. Thank you for taking the time to help us out. It is greatly appreciated.

    That's a great suggestion. Hopefully someone more versed in HVAC can answer your question fully. I am intrigued, in any case.

    I'm not that good with HVAC vut i used to work with a guy that installs them, If you have a look at the outdoor unit, if the connections are condensing water, it would just be a waste but if your refrigerator has the wire on the back, you could have the water move through pipes over them because fridges get colder, use more power and put off more heat. Hope that helps, if u need to know anything else just ask

    If both of the connections on the outdoor unit are condensing water then the unit is probably low on freon and needs to be recharged. On a properly working unit the one of the pipes is cold and the other is very hot. I am suggesting using the water from the indoor unit to cool the one hot pipe running to the outdoor unit. Also, trying to water cool a refrigerator with coils on the back or underneath would require major modifications including elaborate drip pans, splash shields, and in most situations, a pump to get the water to it. This doesn't take into account the extra humidity such a setup would put into the room. I really do not think that would be very practical or efficient. And as for a refrigerator using more power than an central AC unit - there is no way. Refrigerators run on a 120 volt, 15 or 20 amp circuits. Central air conditioners run on 240 volt 30 amp circuits. Also an average size AC unit gives off around 4,000 to 6,000 BTUs of heat whereas a refrigerator only gives off a couple hundred BTUs at most.