Tandem Rain Barrels




Introduction: Tandem Rain Barrels

The purpose of this tutorial is to demonstrate how you can have two rain barrels where the first rain barrel overflows into the second one once it is nearly full.  This is a simple design that I was able implement in 30 minutes once I had purchased the materials.  There are many more elegant solutions for this but I chose this approach because it required the drilling of a single hole near the top of the first barrel and because it provided me with a lot of flexibility in the placement of the barrels.

BTW, this is classified as 'green' because my wife exclusively uses the water for the two 8x12 ft.  gardens we have in our yard.  We never water with a hose.

[Update 1 May 2010] We had a storm last night and got 3/8th of an inch of rain.  When I looked this morning, the second barrel was full and was slightly overflowing down the sides.  I just wanted to make sure that there was no problem with the pipe transferring the water from the first barrel to the second.  In fact, despite the fact that the rain had stopped, water was still dripping from the downspout into the first barrel.  The same amount of dripping was falling into the second one. 

Step 1: Materials Needed

-- 2 rain barrels (preferably PVC used by the food industry)
-- Length of 1/2 inch PVC pipe
-- 2 PVC connectors for 1/2 inch PVC pipe (threaded male end on one side and the other side smooth female)
-- 1 extension connector that is female threaded on each end
-- 1 right angle connector that is female smooth on each end
-- small container of PVC cement (optional)
-- Bricks to elevate the first barrel

Electric drill
13/16 inch drill bit

I paid $30 each for the used rain barrels at a local Indianapolis company.  They come with with a cover that has both a larger and a smaller filler holes with threaded caps.

The PVC materials cost less than $5.

Step 2: Drill Hole in the First Barrel

Drill a hole towards the top of the first barrel in the direction of where the second barrel will be.  This first barrel should be elevated on blocks at least 3-4 inches above where the top of the second barrel will be.

The inside diameter of the PVC will be 1/2 inch but the outside diameter is larger, of course.  I guessed that the size of the hole that I would drill was 13/16 inch.  This proved to be perfect.  It Is just open enough for the connect with male threaded end to grip withing the hole. If you make it any larger, it will wobble around.

Step 3: Attach the Connectors to the Barrel

From the inside thread the connector that has the male threads through the hole until it contacts the wall of the barrel.

From the outside, thread the extension connector to the connector that is threaded through the barrel.  Hand tighten until it is snug.  The water flowing through the overflow connection will not be under pressure and if it leaks at all, it won't be much. 

Step 4: Add the Extension Pipe and Right Angle Connector

Screw the second connector that has male threads on one end into the extension connector.

From the 1/2 inch PVC pipe cut a length long enough to reach a position directly over the filler hole of the second barrel.  I merely slipped this pipe into the smooth end of the connector we just screwed in.

Finally, slip the right angle connector onto the pipe with it pointed down towards the opening in the second barrel.

I did not cement any of these slip-on connectors because I wanted the option of rotating them or of replacing the pipe with a one of different length.  You could also add one final lenght of pipe from the right angle connector down into the barrel but this is not really necessary and it would impede the removal of the lid.

Step 5: Final Result

With my setup, the larger hole in the lid of the first barrel is placed directly under the downspout.  If not all of of the water goes into the hole, it will pool on the lid itself and eventually overflow into the opening.

You can optionally insert a spout near the bottom of the first barrel.  This barrel should be high enough off the ground the permit a bucket to be placed under the spout.  If you also want a spout on the second one, the whole setup is going to have to be raised unacceptably high off the ground.  With a previous rain barrel that we had, we found that the spout filled the bucket too slowly.  That was true also if we connected a hose to it.  With the current setup, my wife said that she would prefer that the barrels be kept lower off the ground and she simple takes off the lids and dips water out of them.   This makes it a much faster operation.

Although I haven't done it yet, will somehow fixed some sort of netted material (such as the bag that onions are sold in) over the openings of each barrel.  This is to prevent debris from going into the barrels and to prevent mosquitoes from breed there.  There is no easy way to do this.  I thought of using velcro to hold the material in place.

You will notice that there is no mechanism for letting the second barrel to overflow in a controlled fashion.  Note that I have calculated that a tenth of an inch of rain will fill one barrel.  If you get a half inch of rain, the second barrel will definitely be overflowing.  For my arrangement, the water simply flows over the top and down the sides.  Since our house is built on a slab, this is no problem for us.  On the other hand, if you feel there is a need to lead the excess water away from the house, just drill another hole in the second barrel and use a similar setup to direct a longer PVC pipe out further into the yard.  

Step 6: A Variation With Three Barrels

I decided to use this technique with rain barrels on a garden we have out in the country.  We have a shed there but no electricity or water.  We put gutters on the back of the shed and installed three rain barrels in tandem using a variation on the technique described earlier in this tutorial.

I decided that, instead of having the first barrel drip into the second one, I would have each barrel flow directly into the side of the next one.  The connectors are the same as before.  I simply cut a 4" PVC section of pipe and slipped it into the two female smooth receivers on each barrel.  If I want to disconnect, I simply pull an outer barrel away from the next one and it slides right out.  There is no need to cement the pipe in.  You can see the results in the two photos.

Lesson learned: These barrels seem to come with several variations in design and I wasn't aware of this until I got them home.  The barrels I used in the main tutorial are squatter but the same capacity of the the two newer ones I bought.  The barrel on the left is of this type.  Notice that it is raised up on a wood platform.  I had to do this because the two newer barrels were taller and the third one had to be raised to meet the pipe coming in from the second one.  Another problem is that the two newer ones have an inward slant near the top.  Drilling a 13/16th inch hole near the top would have pointed the pipe upwards instead of horizontally.  I had to make the hole about 3 inches from the to make the pipe horizontal.  That means that I am wasting some of the capacity.  When you buy barrels for a project like this,  pay attention to the design.

[update 19 June 2010]  I just added another instructable involving the rain barrels at this shed:  https://www.instructables.com/id/Redirect-water-from-a-raingutter-to-a-rain-barrel/
This shows how I directed water from the front gutter to the barrels in the rear using PVC piping.

This shed is the source of all kinds of experimentation.  Yet another instructable shows how we added solar panels to it: https://www.instructables.com/id/How-to-mount-a-solar-panel/.



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    19 Discussions

    Here's a less complicated method of connecting

    Since this is just overflow, there really is no hydraulic pressure. If it leaks a little, no big deal. I didn't have a problem with leaking.

    Instead of using a PVC pipe with a downspout and open drop to fill the second barrel, you could instead have connected both barrels with a length of hose going out a spigot on the side on the first barrel and into a spigot on the side of the second (you of course have to seal the spigots in place with silicone glue).  However, this connection must be made at the bottom of the barrel, rather than the top, otherwise, the first barrel will never drain.  This removes the need for the open hole in the top of the second barrel.  This also allows for both barrels to be at the same height, meaning you could conceivably have as many barrels as you wanted, without having each barrel to be lower than the last.

    As for overflow from the second barrel, you could insert another spigot on the side of the barrel at the top and run a piece of hose from there to whatever remains of your gutter's downspout, effectively draining the water to where ever it went before you had rain barrels.

    The problem with your design, and the cause of the slow rate of fill from your previous barrel is that rain barrels are too low to the ground.  To get a decent and consistent flow, the barrels must be higher than whatever you are trying to water or fill with water.  Unless you hook a pump to the barrels (which to some extent defeats the purpose of them in the first place), the only thing making the water come out is gravity.  Raising the barrels a foot should be adequate to fill a watering can at the same rate a hose connected to a municipal water supply would.

    I implemented all three of these ideas in the rain barrels I built for my parents (I live in an apartment, otherwise they would have been for me) and they've been working perfectly for almost a year now.

    2 replies

    These are very good ideas.  The first barrel is at least one foot off the ground and the output from the faucet I had on the bottom of a whiskey barrel was still too slow.  It would take a minute or two to fill a 2 gallon water can.  My wife prefers being able to lift off the lid and simply bail the water out.  She can fill the water can in a matter of 5 seconds.  The old whiskey barrel had no removable top.

    You are right about having the outputs at the bottom of each barrel and connecting them together with a hose.  I personally hate plumbing and do it poorly.  One reason I avoided putting a faucet at the bottom was that I would have to literally climb into the barrel (with it laying on its side) to work with screwing in the hardware and with making it water-tight.  Using a garden hose to connect the two barrels is also a problem because hose connections are always difficult to make water-tight. 

    There is another design on this website that connects the two barrels at the bottom with PVC and with a faucet in the middle.  That's an excellent design but I didn't want to mess with the plumbing and I also wanted more flexibility in the placement of the second barrel.  A hose would give more flexibility but in the end I went for a design that wouldn't challenge my plumbing skills.

    I have an adjustable wrench duct-taped to an old vacuum cleaner pipe to reach inside the barrels for plumbing.

    My wife fills her watering cans from the top too - but I use a spout on the bottom to drain the barrels each winter and to water my bushes, roses and raspberries (with a soaker hose).

    Each year I'd added a barrel or two; as our water rates keep climbing - I'd love to bury a holding tank underground to keep extra water.

    I too dislike plumbing but the "blue barrels" I have available have two bungs. They both have a 3/4 inch pipe thread in the center of the bung and have a 2 inch pipe thread on the outside.You can minimize plumbing by setting the barrels "face to face" and using pvc to place a 3/4 inch pipe between them with a T and valve in the middle. I use ball valves to increase flow rate. I place a 2 inch PVC fitting in the upper bungs connected with 2'' pvc pipe to permit flow at a higher rate between the barrels than would be permitted by the 3/4 inch pipe alone. I cut a hole in the top of one barrel for the downspout . This provides me with 110 gallons of water from one of my garage downspouts with a rain of about 1.25 inches. Over flow is not a problem in my case but a PVC T could be installed in the upper pipe and "plumbed" to handle this. p.s. Some barrels have a "course" thread on one bung. If this is true of yours, be sure to thread your 3/4 inch pipe into that bung or you will be in trouble when you want to install your 2 inch pipe.

    All of these rain-barrel 'ideas' seem to be the same and they almost all lack a way of vacating the water without siphoning them off one by one. Here's a tip - if you're going to run tandem rain-barrels and drill into the barrel then you might as well drill into them close to the bottom and connect the barrels together along a common header that also has a valve on one end. With this setup you'll never have to siphon them off one by one and they'll all keep the same level even when you're draining them. Raise them up on a couple layers of bricks and you'll look like you're a pro rain-water harvester.

    4 replies

    Thee are two reasons I didn't put a drain at the bottom. The first is that I didn't want to elevate them high enough to get under the drain. The second is that the drain from the bottom is that they fill the can too slowly. I know this from previous experience. With the barrels sitting on the ground, we can dip milk jugs into each of the three barrels and fill them five times as quick. Also, If I connected each at the bottom, then all would seek the same level. This way I can drain the last barrel and have the other two full.

    Alright, I guess you have your reasons. I'm in a desert climate so I'm setting up to harvest and save over 6,000 liters off of my shed roof per year so that I can use it through the drought season. Everybody has their own applications - I have to think on a lot bigger scale for my stuff. I'll be harvesting water off of the roof of my house and greenhouse as well. I'll probably make some type of pond for this though since it will be a real substantial amount of water.

    Sounds like you need a more serious solution. A pond in not a good idea because of the evaporation. What about burying a water tank that can hold a greater capacity?

    That's starting to get really expensive to have a large buried tank. I know there'd be a fair amount of evaporation with a pond so I was thinking semi-covered. One end of the pond would be completely covered and the other end would have plants in it to help the sun from hitting the water. With the pond, the water can stay 'living', I can actually have plants in it so that the water stays healthy. Right now it's just a thought as I'm sticking with my very large tanks for a bit here.

    Neat!  What I was thinking is that it would be possible if you lived in a place like San Diego where all the rain comes in one or two months, you could make a series of rain barrels and collect it for the ten months you got nothing.

    A more simple solution is to take a short piece of garden hose that will reach the bottom of both barrels. fill it with water, hold it with your thumb and put it to the bottom of the second barrel.  Both barrels will need to be the same height. As long as you dont drain them below the bottom of the hose they will always level to each other with the siphon.

    1 reply

    Been there, done that.  One or the other barrel always gets emptied to the point where the syphon is broken.  That's actually what moved me to come up with this solution.

    Great idea. I've never used a rain barrel before, not really having a use for one before, but now that you've said you use it for your garden, that makes perfect sense. I feel so stupid now... Thanks for the idea

    1 reply

    I remember when I was a kid my mother would have me collect rain water from the downspout so that she could use it to wash and rinse her hair.  Even now it makes sense because tap water contains all kinds of chemicals and calcium which isn't good for the hair.  Where do you think the shampoo product 'White Rain' gets its name from?

    Is that overflow pipe from barrel 1 to 2 large enough? There is going to be too much friction within it considering is so close to the top and therefore has low pressure or almost none. Also the downpipe from roof is presumably of a much larger diameter. The overflow to the second barrel is not going to be fast enough during heavy downpours and you will loose a lot of the water. The first barrel will fill up faster than it can overflow to the second.

    1 reply

    You are probably right on this but in the end it doesn't matter.  If it is a heavy downpour, much more rain will come down than will fit into the two barrels together and the excess will be 'wasted'.  If I had to worry about where the excess would go, I would maybe put in 1 inch piping and then direct the excess from the second barrel further out into the yard.  Anyone who decides to adapt this design should worry about where the runoff goes if there is a problem with the runoff staying near the house.  In my case, the original downspout dumped into a runoff pan that was only two feet long and shunted the excess toward the yard.  Our houses are built on a 'pillow' so that all the land leads slightly downhill from the house.