Self Watering Garden - Using Recycled Water From an Air Conditioner





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

About: 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 awhile, but another hobby is high powered rockets.

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

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...

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...

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...

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...

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...

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!

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.



    • Water Contest

      Water Contest
    • Stick It! Contest

      Stick It! Contest
    • Backpack Challenge

      Backpack Challenge

    62 Discussions

    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.

    1 reply

    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,)

    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

    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!


    3 years ago

    Thank you

    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.

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

    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.

    2 replies

    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.


    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.

    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.

    2 replies

    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.

    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.

    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?

    2 replies

    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.