Introduction: Self Watering Garden - Using Recycled Water From an Air Conditioner

Picture of Self Watering Garden - Using Recycled Water From an Air Conditioner

Did you ever notice that your central air conditioner has a hose that connects to the drain? I never really thought about it until one night I almost tripped because ours went across the basement floor. I cut the hose and placed a trash can there to collect the water... I figured that I would just dump it each day.

I was surprised the next day to find that it had filled the trash can and made a fair sized puddle on the floor, and quite a mess with a stack of papers that was sitting there. After some rough calculations I discovered that about 350 gallons (1300 liters) was being wasted annually. (And that was a conservative estimate!)

I decided to install a pump and use this water for my small garden which was right outside the basement door. All I needed was to figure out how to spread the water evenly for the plants.

We have used this system for several years now... as soon as we move into our new home we will install the updated version described here.

Step 1: The Original Design

Picture of The Original Design

I actually built this unit in April of 2000, so I have been enjoying fresh vegetables every year for quite awhile now. As well as the original design worked there were a couple of drawbacks to presenting it here as an instructable.

The cross pieces on the original unit were made from a 4-way Tee section that I had modified on my lathe. Since not everyone has access to a lathe to machine the parts, and because I am getting a new house and will rebuild the system anyway, a new way of doing this was devised.

Another change that was made was the area where the water left the house and went to the A-Frame... I had used flexible tubing but after a few years it became brittle in the sunlight. I switched to ridged PVC, but this made the unit difficult to move around. Both of those problems were solved with the new design.

Step 2: Starting at the Air Conditioner...

Picture of Starting at the Air Conditioner...

The first step is to install what is called a condensate pump to get the water from where it is now to where we want it. The pump has a built-in tank and a float valve. When the tank is about 95% full the pump will come on and continue until the tank is empty. Depending on your pump this will usually be about a gallon (4 liters) at a time.

This really works out well because instead of your plants getting a great deal of water once in the day... they get a small watering several times all day long. Since the water is from an air conditioner it tends to be very cool... this helps keep the plants from overheating too. Before this project I could barely keep the plants alive... now... I have to cut them back all summer!

The pump is placed lower than the output of your air conditioner system and a flexible tubing is run from the pump to the wall where we drill a small hole for the connection to the outside.

Step 3: Run the Tubing to the Outside Wall...

Picture of Run the Tubing to the Outside Wall...

Once you get the pump installed you will need to run some flexible tubing from the pump to the place where you will exit the house to the garden. On the original project we just drilled a hole in the wall and put the hose through it. This worked great for the first year, but then the hose we used cracked (outside) from exposure to the UV from the sun. In this version we will connect to a brass hose connector and run outside... then connect to another hose connector. This will allow us to have flexibility and easy repair should the outside hose ever need replacement.

Be sure that the path you take from the air conditioner to the outside wall does not lay directly on any electrical boxes, lights, or run across anything that could melt it such as the flue for your heater. Likely you won't have any problems finding a good path, but I wanted to be sure the design is safely installed!

Step 4: Moving Outside...

Picture of Moving Outside...

Once you get the hose to the place where you want to go outside, we need to drill a hole and provide some sort of path for the water that allows us the ability to disconnect the hose for maintenance, and that does not allow insects to enter the building.

The original design just had the hose outside, then it was updated to rigid PVC which worked but was not as easy to relocate and maneuver. The new design is very flexible and the whole unit can be moved to allow you full access to your garden if you need it for weeding and such.

We used a fitting designed to go onto a 1/4 inch ID (6mm) pipe nipple long enough to penetrate the wall and leave some threads out. We didn't want the fitting to scratch up the paint on the wall but we wanted to be able to really tighten it down to keep it secure and keep insects out.

The design was simple... add washers and tighten down the fittings to sandwich it all together into a solid attachment point for the hose.

Step 5: Let's Build a Frame...

Picture of Let's Build a Frame...

So now we have a source of water outside, let's do something with it. The A-Frame is built from 2 inch (60mm OD) PVC pipe. The result is a very sturdy design that does not need the use of anything more than PVC glue and a hand saw to construct.

Once the two side units are assembled the water tube is press fit (friction fit) into the top Tee connections. As it works out... the fit is very good.

Step 6: The Water Bar Assembly...

Picture of The Water Bar Assembly...

So you have the A-Frame built or you have another existing frame that you can suspend the water bar from... now we need to build the bar.

The bar is very easy to build, simply cut your two long peices to the proper length and glue them into the Tee connector as shown.

Glue the two end caps onto the tube and allow to dry.

Drill a series of 1/16 (1.5mm) holes evenly spaced every 2 to 3 inches (50 to 70mm) down the length of the pipe. If you use a slightly larger diameter drill, say 1/8 inch (2.5mm), then space them every 6 to 8 inches (150 to 200mm) apart.

For tomatoes I used a 6 inch (150mm) spacing... for beets and peppers I used 4 inches (100mm)... it's not that critical.

If you hang the water bar from a structure you may need to support the feed hose so it doesn't move the bar off-axis. It's good to use a level to be sure everything is watered well and evenly.

Step 7: Enjoy!

Picture of Enjoy!

That concludes the construction of this project... now you are ready to plant your flowers or veggies and enjoy the benefits of this automatic watering system. I was going to calculate how much energy the system uses... but frankly I never saw any noticeable increase in the utility bills. I did notice that our water bill was almost 10% lower from not needing to water the plants daily.

All in all this was a fun and benifical project... it saves precious resources, makes you work less in the garden, and because the water contains no chlorine... your vegetables taste much better and the plants don't yellow as much.


DarronC1 (author)2016-09-16

HVAC condensate is an excellent source of relatively clean, chemical free water for non potable use. However, I caution you against spraying the water. It is possible for the water to pick up microorganisms when it comes in contact with the AC coil. Legionella is a particular threat. Spraying the water can release these into the air where they can be breathed in. If used for irrigation, the water should be used in a subsurface or drip system.

askjerry (author)DarronC12016-09-16

Yup... drip only... the PVC is not pressurized, with holes drilled in it at regular intervals... strings carry the water to the ground. I don't live there anymore... but it has been in continuous use since about 2001 or so. (I think that's when I built it... LONG time ago,)

JohnT327 (author)2016-07-19


JohnT327 (author)JohnT3272016-07-19

Please be careful .that water has high amounts of lead in it.if your teeth are turning black your poisening yourself.a test kit and fiktering may help but be dilligent and careful it may be building up in you

federicoaltuna (author)2015-04-05

I have some doubts I would like to discuss with you. I have had an idea and now I see you are ahead of me. I would appreciate an email if you have any interest. Regards!

q8wii (author)2015-01-01

Thank you

DanTDM (author)2014-01-24

Cool. Use grey water too

mcounter (author)2013-02-11

I like your idea of recycling your air-conditioning water for watering your garden. Recycling water in your grow room is a viable option for hydroponic growing. I have found here some simple procedures of recycling water with your existing hydroponic systems in your garden.

tinker234 (author)2012-02-16

could i add a cheap water filter for the plants

askjerry (author)tinker2342012-02-16

Possibly, just remember that this water is not under pressure as your indoor plumbing would be.

tinker234 (author)askjerry2012-02-19


icarson (author)2011-04-28

Using weeper hoses you would lose less water to evaporation as well as getting rid of the frame above the garden. The weeping hose cost far less than the pvc piping.

I use the pump to get it into the rain barrels and then have the weeping hose attached to the rain barrels and let it out as needed.

askjerry (author)icarson2011-04-28

Possibly, but there is also the potential for them to get clogged. This water has no chlorine in it to kill off algae and such... so it could grow in/on the hose and clog it up. The system I built has tiny (1/16 inch) holes on the bottom and larger (3/8) holes on the top so I can poke them with a cleaning tool if needed.

Evaporation never seemed to be a real problem... the ground was almost always wet or moist and since I mixed in a fair amount of gypsum and sand with the soil... it gets wet pretty deeply too.

But your method could be a viable alternative... let me know how it works out for you.


icarson (author)askjerry2011-04-28

The weeping hose is buried 8' down and surrounded by gravel, so no light and algea growth. feeds the water right to the roots. Has worked great for 4 years, knock on wood, spring is finally here, and don't want to jinx it.

magickaldan (author)2010-05-09

This is fine for non-edible plants only if  you plan on eating the plant Don't try this!  You can get all kinds of nasty diseases Your AC sucks in all kinds of dust and bacteria such as the flu virus and one of the biggest ones is Legionnaires' disease.

blucolt (author)magickaldan2011-04-19

you're spot on, but your reasoning is bad. the reason to not use this system for edible plants is because some AC units have heavy metals (including lead) that can leach into the HVAC water. You won't catch the flu virus or Legionnaire's from plants, only from inhaling colonized droplets.

askjerry (author)blucolt2011-04-19

In this case, the water is running down to the ground through the strings at the bottom of the watering holes. The plants then absorb the water from the ground.

Some water will of course splash on the tomatoes... but they are washed thoroughly prior to consumption.

phillipt (author)2011-04-12

I don't have much experience gardening, but my wife and I are starting a "container" garden on our balcony. Our HVAC is installed such that the rear of its closet is to the outside of the condo and on the balcony -- that is, the condensate outlet is already outside and we can very easily implement this system.

What about over-watering? or under-watering? If by chance we under-watered, we could always supplement it the good ol' fashion way.

Could over-watering be a concern?

askjerry (author)phillipt2011-04-12

I doubt that over watering will be an issue unless you live in an area of very high humidity where the garden can't evaporate properly. If that happens, just install a diverter valve to dump the excess away from the plants.

As far as under watering... I had to water the plants sometimes... but not nearly as much as before the system was implemented.

phillipt (author)askjerry2011-04-12

Thanks for the tip and quick response.

dripwater (author)2010-10-06

Check out for a complete A/C condensate irrigation system and additional answers to yoour questions

CyborgGold (author)2010-08-17

Great Idea! If you want it to be a bit more visually pleasing, you could look up an instructable on how to make PVC tubing look like Bamboo! (It looks amazing)

askjerry (author)CyborgGold2010-08-17

Great idea... I found it... Thanks for the tip! Jerry

AmyLuthien (author)2010-04-11

Another advantage to using the black hose outside is that algae doesn't build up in it ;) (author)2009-04-16

Awesome project. We can dump about 120L a day from our dehumidifiers if we leave them on 24x7, and I've been looking for a way to use it. Has anyone thought about mineral leach though? It seems like the condensate should be pretty much distilled water. Should I be adding extra plant-food somewhere in the system?

RoBear613 (author)adam.read2009-05-27

I'd either use a slow release fertilizer as an amendement when I plant (first choice) or use a liquid fertilizer periodically. Injecting fertilizer into the condensate could result in too concentrated a solution, harming your plants. And most fertilizers aren't meant to be applied continuously. Plus, not all PVC is chemical resistant, which could possibly lead to PVC contamination of the soil (and the food).

askjerry (author)RoBear6132009-10-24

Every year we dig up the bed and remove old roots and so forth. In the spring we generally add some fertilizer and vermiculite to the soil as well as perhaps a bit more soil to replace what was dug out. So it doesn't really seem to be an issue. It's been running for nearly a decade with big crops every year.


A good name (author)2009-03-30

Bad for your health for PVC's to be near your food.

askjerry (author)A good name2009-03-31

Here in the USA we have PVC plumbing in most houses already... this is for our drinking supply. The water sit in the plumbing for hours and/or days before we turn the faucet. The water from the AC unit and goes into the system briefly... 10 to 30 seconds, then to the ground, the plants absorb from there. I think the water that flows through the house plumbing contains metals as well as clorine, flouride, and other materials would likely be worse for you than the condensation water that only briefly passes through 20 feet of PVC for 30 seconds. Additionally, I think the runoff from the roof and through the rains pouts (also PVC) would be much worse... birds leave droppings on the roof... which may contain disease. The water from the AC unit should be better... I would not call it potable water, but for irrigation it should be fine. There are terra cotta flower pots... but I have seen many made from vinyl... which is a form of PVC... vegetable seedling pots are often ABS or vinyl as well. If you are still concerned, the unit could be constructed from copper plumbing parts, or even galvanized steel. I'm not sure chemically... but I think I would prefer the PVC to the galvanized steel... not a chemist... so that could be debated. Jerry

SeaEddy (author)askjerry2009-10-23


chuckr44 (author)A good name2009-05-21

No, the bad plastic (bad additives called phthalates and BPA, actually) comes from the #7 plastic.

PVC is fine, unless it is heated to melting point where it gives off fumes.

girardot (author)2009-08-25

This looks nice. I have an AC unit that dumps about 4 to 5 gallons of water on a hot day. I was thinking of a way to use that to water my lawn.

cwopdog (author)2009-07-25

I like your idea, I have a 4 ton unit here in S. Fl. and it puts out a lot of water. I plan to incorporate your ideas to water plants and I also have a float pump to spray fog misters on the outside of the condenser unit that draws in the cool air. I put an amprobe on one of the 120 volt phases and measured about 13 amps while the comprossor was running. After turning on the misters, I saw the current drop to 10 amps! This lowers the head pressure and allows your compressor to run a bit more efficient. The condensate is ideal as it is essentially distilled and doesn't tend to cause mineral scale to form on the coils. There are many qreat tricks out these to help save money and cut waste, Best of luck to you and your projects!

OnlyUsernameAvailable (author)2009-07-03

Excellent idea. Recycle, use PVC,...couldn't get better than that!

dlw (author)2009-04-21

That is a great idea! I wonder if you pumped the water into a small tank at the garden and watered via drip irrigation. You would not loose water to evaporation when you spray it and it can help keep your plants dry (can help with fungus growth). Again, really great idea and design!

chuckr44 (author)dlw2009-05-21

The drip irrigation hoses I am familiar with require water pressure. They do not work with gravity fed systems. This is basically a gravity fed system assisted by a pump to get the water "upstairs" or over a hump. After the water is over the hump, the water is gravity fed.

askjerry (author)2009-05-06

We did add fertilizer to the soil at the beginning of the growing season... the location was just a hole in the cement at first... we dug it out and put in some good soil. As for the plants and minerals, etc... the tomatoes we got every year were always very good. We don't spray them with pesticides which i think would be far worse than anything from the system. Also... the diseases mentioned like Legionnaire's were caused by water in a cooling tower... this is water outside that is pumped over and over cooling vanes... it usually has high levels of chlorine added to kill the bacteria... in that case it was improperly maintained and allowed the growth of the bacteria... there were other issues with the circulation, etc. Not a factor with this design. The water comes out of the AC and is pumped immediately outside where it drips into the soil and disperses. The plants get the water via the roots which act as a natural filter... since the water contains no chlorine, bromine, etc... the plants are VERY healthy. The plastic owl was stuck there for show... it was given to me by a friend because it looked good. All I can say is that this system was installed around 2001 or so... (if memory serves me...) we have never had any problems with any of the food. If this concerns you... then just use the water to grow flowers... it is still a good way to use the water instead of throwing it away. Dehumidifier... yes... that would work as well... pump it out to the plants! GREEN! Jerry

its a lion (author)2009-05-06

We do this. Except instead of going to plants like that, it runs down to a tree with a few flowers planted around it. We have it dripping into a pipe with a hose running underground out to the plants. Seems to work quite well actually. The tree has grown roughly 15 - 20 feet in around 5 years.

Gaglioti (author)2009-05-01

Another great idea for me to work on at home. I love this concept and all the other creators that take the time to show us. Thanks!

killbox (author)2009-04-25

Sadly out here in the desert, we rarely get more than a cup or two of water from our ac-units. and we are more likely to have (Evaporative coolers aka Swamp-Coolers) anyway.

vger13 (author)2009-04-24

i would be very careful of this water it may be ok for the plants as long as they are not for consumtion.i have been in the hvac and plumbing line for going on 30years,this water is very bad this is where Legionnaires' disease originated. i wouldnt want this water near anything i am even handling

sofficinifindus (author)2009-04-16

good work... but plants don't love water from air conditioner (like demineralized) they prefer rain ;-)

schwally (author)sofficinifindus2009-04-16

Demineralized? Last time I checked, your soil supplied the majority of that. I would agree that they prefer the rain, but only over tap water. Plan is good, but what I would do is us the KISS method. We send the hose into our sump pump. Sump pump empties into our rain barrel system, along with the eve trough. Connect a hose to our barrels (about 220 gallons), and use this for all our watering needs. (author)schwally2009-04-17

This is what I was talking about. Rain and tap water have minerals dissolved in them, but the condensate won't. Will constantly putting distilled water on a garden bed wash the minerals out of the soil? Does anyone know how this will affect the plants?

Silence (author)adam.read2009-04-23

Thats a point that struck me almost right away on this one. While this may eliminate or reduce the need for watering, aircontitioning and dehumidification systems by nature produce distilled water (condensed from the air in the house), normally devoid of minerals and nutrients that plants require for healthy growth. If your plants are outside and in the earth then you have little to worry about, but a little fertilizer wont hurt. If your feeding potted plants then the soil eventually has to be fortified with fertilizers to keep the plants growing healthy. What happens when they dont have the nutrients they need. First they dont grow as tall or have as much foilage if they grow at all. The plant needs foilage, so it diverts its efforts to leaf growth and and less to fruit growth. Slender stalks wont hold those prize winning tomatoes either. To increase yield make sure they get fertilizer. In the garden back home, my dad tills in cow manuer every year, we get plants that stand 4 to 5 ft tall, one year we had so many huge tomatoes we didnt know what to do with em.

annarch (author)2009-04-23

I just want to know___ does the plastic owl really work???

Dzakovich000 (author)annarch2009-04-23

It will scare some animals away, but after a while, they realize that it has been sitting in the same spot for a couple of weeks, and ignore its presence.

jeff-o (author)2009-04-23

Hmmm, my high efficiency furnace drains water once in a while (yes, it's true!) - I wonder if that water is suitable for watering plants? It would have to be indoor plants though, since the furnace (naturally) only runs in the winter...

codwithchips (author)2009-04-23

Hi jerry, i like it you go for mabe try reuseing water of washing machine

About This Instructable




Bio: I like to create YouTube videos and have a channel. I also like to work with CNC, electronics, and I build robots. It's been ... More »
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