DIY Project: Rain barrel water collector


If you have a roof, and it rains, you can collect and store rain water to improve your resilience. Having extra water increases your drought tolerance, extends your watering window, and may even save you some money.

Note: This assumes you already have gutters and downspouts connected to your roof, to move the water away. If not you will need to set those up first, which is big enough to be its own project.

Where Rain Water Collection Is Legal

Strangely, some countries allow collection of rainwater, and some do not. Check your country or local laws to confirm, before you begin. I collected a list of links and countries at the end of this article; updates or additional sources are welcome.

Tools You Need

  • A drill
  • A level
  • A pencil
  • Safety goggles

How To Do It

You will need a rain barrel, a sturdy base to stand it on, and a diverter to get the water from the downspout into the barrel. The diverter is the trickiest part, but I’ve done the research so you don’t have to.

The Barrel

flickr_rain_barrels_jennifer_c_cc-by_2.0[There are many different styles of rain barrel to choose from. Photo credit – Jennifer C on Flickr. Licensed under CreativeCommons CC-BY 2.0]

You want a food grade barrel. Depending on your goals and budget, you can often find these for free on craigslist or from local restaurants and food supply stores. You can also buy them at hardware stores. Some cities and counties have water barrel programs where they may give away or sell you barrels at a discounted rate. Check your local water utility.

I sourced a free barrel from a neighbour but it was not opaque. I wanted an opaque barrel so no light would get through to reduce algae growth. I ended up buying one from the hardware store.

A Closed Top

I prefer a barrel with a closed top, so mosquitos and critters can’t get in and breed or drown. Some barrels come with hatches. I assembled a hatch cover using some plastic and some old landscaping cloth, to keep sunlight out.

The Base

One gallon of water weighs 8.3 pounds or 3.7 kilograms. A 55 gallon barrel of water weighs 460 pounds, or 208kg. You need a sturdy base to hold this weight.


I used the following layers as a base:

  1. Sand on the ground, below the base. Make sure this is level before you start.
  2. 24” square cement pad. These might be called “paving stones” or similar names, depending on where you get them.
  3. Four standard cement blocks. These measure 8” bx 8” by 16”, so if you fit them into an “L” pattern you can put an 8” side and 16” side together to perfectly cover the 24” pad.
  4. A second layer of cement blocks to raise the barrel up. This increases the water pressure, and is tall enough that you can fit a standard 5-gallon bucket under the tap
  5. A second 24” cement pad on top

Make sure your base is level again, then set everything into place.

The Diverter

The diverter moves the water from the downspout into your rain barrel.

I spent thirty hours researching eleven different models of downspout diverters. In the end I chose the EarthMinded FlexiFit diverter.

I chose this diverter model because:

  • You only need to cut one small hole in the side of your downspout
  • You do *not* need to sever the entire downspout. So if the project does not work out, you can simply plug up the hole (plug included) and move on
  • The diverter fits many sizes of downspout. Depending on where you live, your downspouts may be square, round, rectangular, and many different sizes -2”x3” , 3”x4”, round 3 to 6”, K-style, etc. The EarthMinded diverter is made of flexible, UV-resistant rubber (EPDM) so it can change shape to accommodate your downspout. Even if it doesn’t fit exactly it can still collect *some* water. They do also sell a round model for round downspouts.
  • The diverter automatically handles overflow, so you don’t need to do anything. When the barrel is full, water flows back up the attachment hose to the top of the diverter. Any more rainwater then simply continues on through a hole in the diverter and down the spout. You don’t need to worry or adjust anything when it rains or stops raining.
  • The water barrel system stays closed. Because the water flows in from the side, you can use a closed top barrel. This keeps out mosquitos, keeps out sunlight so algae doesn’t grow, and keeps animals from crawling into your barrel.

I prefer to buy from the company themselves, but you can also sometimes find this diverter at big box stores or hardware stores.

The EarthMinded installation video is pretty clear. Around 3:38 you can see how the diverter fits into the downspout. Because of surface tension, rain running into a downspout clings to the inside edges of the material. This diverter collects water nicely and funnels it into the connecting hose.

EarthMinded_FlexiFit_Diverter_Install_2_500x438[The EarthMinded “FlexiFit” diverter is made of flexible rubber, and fits into many different sizes of downspout. Once the rain barrel is full, excess water flows through the hole and away normally.]

earthminded diverter screenshot - installation video

Screen shot of EarthMinded diverter in cross-section of downspout – from their installation video.

Setting It Up

Now that you have all of your parts the procedure is fairly easy.

  1. Assemble your base, and put the water barrel on top.
  2. Make sure the connecting hose can reach from the downspout to the barrel.
  3. The important part is: make sure that the hole in the downspout is lower than the highest water level of the barrel. This is what makes the diverter work. If the hole in the downspout is lower than the top of the barrel, then once the barrel is full, water will push back into the connector hose and down the downspout, to continue away on its journey. If you attach to the downspout too high or too low, this won’t work. See the image below.
  4. With your barrel in place, use your level to mark where the diverter should go, and where to drill the hole. If you have a short level, you can use a 2×4 or wooden board to help measure.

attachment height

Image from the manufacturer instructions. The diverter hole in the downspout must be cut _below the highest water line_ of the water barrel. This ensures that water will flow back down the connector hose, and into the downspout, once the barrel is full. e.g. If your barrel has a hole in the top or front, the downspout must be installed at a level _below_ those holes.

The EarthMinded kit comes with three circular saw blades for your drill – these are the sizes needed for the tap at the bottom of the barrel (small), the connector hose in the barrel (medium), and the diverter in the downspout (large).

I like to drill the hole for the connector hose in the barrel first, about 2-3” from the top of the barrel. Then place the barrel on the stand and measure a level connection for the hose. This tells me where to drill into the downspout.

Once you have drilled your hole, connect it up. If you have a garden hose you can test the diverter works by spraying water onto the roof.

How Much Water Will You Get?

You need to know:

  • How big is your roof?
  • How much rain do you get each month?

One inch of rain on 1,000 square feet of roof collects 623 gallons of water. That’s enough water to fill more than 11, fifty-five gallon barrels. The pitch of the roof doesn’t matter. So multiply your roof’s square footage by 0.623 – that’s how many gallons you will get from one inch of rain.

In metric: one millimeter of rain on one square meter of roof collects one Litre of water.

Rainwater collection calculator here: https://www.watercache.com/resources/rainwater-collection-calculator

I have to put my barrel away during winter, so I only count rain received during the summer months.

If you have multiple downspouts, choose which one(s) you will use to install a barrel. Consider whether you want the biggest roof area, the closest spout to your garden or where you will use the water, or other needs.

How Many Barrels Do You Need?

flickr_rain_barrels_pete_favelle_cc-by-nc-2.0[Photo by Pete Favelle – licensed under Creative Commons CC-BY-NC 2.0]

One way to estimate how much water you might use is to calculate 0.5 gallons per square foot of garden space, per week.

Another strategy is simply to look at the space you have and how many barrels you could fit.

Starting with just one barrel is a fine plan. Use it for a season and track your use. How often do you empty the barrel? How often does it rain before you use all of the water? You can decide whether you need more barrels in more locations.

What Can You Use It For?

You shouldn’t normally drink rain water that has been collected into a barrel without properly filtering, cleaning, and processing it first. Main non-potable uses include watering your garden, watering trees or perennial fruit, or flushing toilets.

Return On Investment (ROI)

So how well does a water barrel pay for itself? The biggest factor will depend on where you get your barrel. If you find a free barrel from a local restaurant versus paying $200 for a fancy barrel from a big box store, that will obviously affect your ROI.

Based on rough pricing and some rounding, I find the following costs for these materials:

  • Barrel: $0 to $150, depending
  • Cement pads: $15 each * 2 pads = $30
  • Standard cement blocks: $5 each * 8 blocks = $40
  • Water diverter kit: $50 with shipping

That gives a base cost of $30 + $40 + $50 = $120, plus what you spend for the barrel.

You will also need to know how much you pay for water. In many places if you are on metered city water they charge you not only for the water you use, but also a “drainage fee”; so you are charged two amounts for the same water. All the more reason to install these barrels!

All-in-all – In my area with my roof sizes, yearly rainfall, and price for water, a rain barrel should save me $20 to $30 per summer in reduced water use. At a cost of $120 for the base, this means the project pays for itself in 4 to 6 years. If you pay another $120 for the barrel itself, the project pays itself back in 8 to 12 years.

Personally I am happy with a 6 year return on investment that extends my drought tolerance and allows me to make good use of a free resource that would otherwise flow away. If the price of water goes up in your area, this would pay for itself even sooner. And if you are counting on this water to water your garden, water perennial food or fruit, or serve activities like flushing toilets during water restrictions, it is even more valuable. You will have to decide how much peace-of-mind and improved water security is worth for yourself.

I would love to hear about your rain barrel project!

(edit after posting: Corrected bad wording about “being level”. The important part of setup is not to “make sure the connector hose is level”, but rather: ensure the connector hose attaches to the downspout at a level *lower* than the highest water mark / highest water line of the rain barrel. This is what makes the water stop filling the barrel, and begin to backflow into the downspout, continuing on its journey. Thank you to community member Robert Larson for the questions and help identifying this incorrect phrasing.)

More Info

Laws On Rain Water Collection

  • Collection assessment – Australia, Brazil, China, Germany, and Singapore all allow and encourage collecting and using rain water.
  • United States – collection laws by state
  • The UK, collecting rain water is legal so long as it is kept separate from main drinking water
  • Canada (link to PDF) – legal to capture for use flushing toilets and surface irrigation
  • Japan – encouraged in many areas, with subsidies available
  • Belgium (source1, source2) – Rights to using and collecting water protected in the Constitution, with no legal requirement to connect your home to the local water distribution network. Many municipalities offer rebates for installing rainwater collection tanks.

  • Best Replies

  • Comments (17)

    • 7

      You did an excellent job with the execution of this project and the write up for all of us. 

      So far, is there more rain falling on your roof than you are able to use, or can you keep up with what this system produces?

      I’ll be curious to follow up with you in a few months to see if this meets your needs or you want to expand to another tank. Can you just drill another hole into the side of one tank and connect another one?

      • 6

        Excellent questions!

        >if this meets your needs or you want to expand to another tank

        This project has suddenly made me extremely greedy, and I immediately want to install a large 500,000 gallon cistern or storage system. Unfortunately, I don’t have the space for that. I will intentionally stop with my current setup and use it for the season, carefully tracking my water use and collection. I would love to add one or two more barrels, but that will have to wait as budget and physical space allow.

        >is there more rain falling on your roof than you are able to use, or can you keep up with what this system produces?

        The barrels fill up quite quickly! It is more than I can use at one time, but I suppose that is the point. I only have a small garden space, less than one hundred square feet. Watering just the garden alone it would likely take me several days or weeks to use all of the water from full barrels.

        Last year I planted a dozen trees and perennial fruit bushes. During the height of the summer heat I was easily using 100+ gallons per day watering them to keep them alive.
        So while my regular average use may not use all of the water, I may still need more when it’s hot. And hot weather seems when it is most likely that water use is difficult, expensive, or restricted.

        Currently I feel that having something is better than having nothing, and now I have something. It is a start.

        >Can you just drill another hole into the side of one tank and connect another one?

        Yes, exactly as you say. I believe this is quite possible and doable, though I haven’t done this myself. I believe the main decision is: do you want to attach the barrels together at the top (so that the first one fills completely before water moves to the second barrel), or at the bottom (so that all barrels fill equally in volume at the same time).

        The roof areas I have available are several quite different sizes – one is 400 square feet while another is 90 square feet. I would prefer to add two barrels to the 400 square foot area and not bother with the 90.

        Is a rain barrel setup useful in your area?

      • 4

        That is a smart idea to learn what you use this season and save up for another barrel for next year. 

        I like that your barrels are black so they should stay warmer and able to function for more of the year. That would be my concern where I live. Perhaps you could install a solar powered chicken bucket water heater so that it never freezes and you are able to keep water all year. But you don’t really have a lot of things to water during the winter and it would just fill up once and not be used. So using it just during the spring-fall sounds like the best strategy.

    • 7

      Follow-up: I was asked about different roofing materials, and which are suitable or unsuitable for rain water collection. With some brief searching, I find some rough suggestions on roof materials:

      Clean, Good Roof Materials for Harvesting Rain Water:

      • Aluminum
      • Clay
      • Concrete
      • Standing-seam metal
      • Solar Panels
      • Steel
      • Terracotta
      • Tin

      Okay, Acceptable Roof Materials:

      • Corrugated Metal – can be okay, but test your water to see if it contains too much zinc. You don’t want to drink that, and too much zinc can kill plants
      • Asphalt – can be okay. Several sources suggest not harvesting until after the roof is three+ years old, to avoid roof adhesives mixing into the water. Older shingles (especially before 1980) may contain asbestos, which is no and bad.

      Caution, check and test:

      • Cedar shake: Test any wood shingles for fire retardants, you don’t want to drink or use that
      • Copper: May be okay to drink? But copper is a natural herbicide, so don’t use it to water plants
      • Lead flashing: no
      • Biocides: Any roof using zinc- or copper-treated shingles

      Apparently there are special roof coatings you can apply specifically to make it safe to collect rain water.

      Source 1
      Source 2

    • 5

      Great project and write up!

      I’d pieced together rain collection barrels in the past (we currently have 2 functioning), with the water dumping into the top (through several layers of screening) and then having an overflow pipe. I recently ordered one of the EarthMinded kits (at your recommendation) and it looks like a solid kit and it’ll be much easier to incorporate (no need for an overflow pipe — which is just a hassle). 

      I have a 550 gallon cistern that’s just been sitting, waiting for 2 years for me to incorporate it into my rain collection — this is giving me the motivation I need to finally get it done! I just need to figure out how to make a solid base without having to build anything permanent. 


      • 3

        Trace, that cistern is usable on level, smooth, firm ground, just get basic parts & valve for the lower outflow to size down to a garden hose. The weight of water alone will allow decent flow for buckets or irrigation in an emergency. I have one & it’s great. Also you can put various small pumps on that outflow if desired. It would be a big expensive project to put a sufficiently strong base. 

      • 1

        Huh. Hadn’t really thought of that. I guess the weight of the water would be enough to allow some water pressure. Do you have a small pump on yours? Do you have any recommendations? This is water we hope to use regularly. 

      • 4

        I don’t have a pump yet as the tank just sits in tree shade as emergency water backup. I do drain it yearly & it empties easily within a few hours with long hose running to trees. I believe a “transfer pump” is what would be used if desired at the lower outflow, probably added in just in front of your garden hose & after /the shut off valve. Here’s a really budget friendly version that runs off your rechargeable drill. Probably not super durable…  

        Another option that runs off a battery, likely to work longer for you:

        Anybody else have knowledge or experience on that use?

      • 4

        Thanks! I wasn’t even aware things like that were available, now I have a path to follow.

      • 4

        You’re welcome! Extra water is a fine thing to have!

      • 1

        Thanks a lot for sharing this, CR. This looks like a solid setup, and it’s great to know the weight of the water itself makes a cistern of this size quite usable.

    • 2

      Project Follow-up, several months in:

      I have been running this system now for several months now (I had it set up before I had time to post this post). Some things work well, others need improving.

      1. Overall: The system works well. When set up and installed correctly, the diverter, gutter, and rain barrel system catches and stores water. I can use the water as needed. This is great.
      2. *Really* make sure your connector hose is attached to the downspout below the highest water line of the barrel. On one barrel I cut into the downspout a bit too high. This was the first one I set up, and I was still learning. You really do want to make sure the connector hose will attach _below the highest water line_. My rain barrel model has a ‘bonus’ hole in the top front. I thought my measurements were correct to place this. However, once installed it quickly became obvious that the downspout was attached above this line, rather than below. When it rained, water would spew out the front of the barrel, as water always exits at the lowest point. Not what you want. I had to drain the barrel, disassemble the base, add extra sand underneath to raise it up, and then re-assemble.
      3. The plug doesn’t plug. I am disappointed in the quality and shape of the downspout hole plug. If you need to disconnect the system (see above), especially during a heavy rain, the plug does not actually plug the hole 100%. Water still sneaks around the edges and travels outside the hole in the downspout. In my case I got lucky – surface tension causes this leaking water to stick to the downspout edge, run down to the elbow, and then pour back in to the downspout where the system goes flat and out to the ground. However, the plug really should plug. I have contacted the company to ask about this, what can be done, and if there is a replacement better plug. I may have to craft something (e.g. silicon rubber, or similar).
      4. Long connector hoses sag.

      One of my barrels is set up at nearly the maximum of three feet away from the downspout. During heavy rain, and once the barrel has filled with water, the connector hose sags:


      This likely prevents it from working well.

      Taking inventory of materials I had, I created a very hacky fix for this using a chunk of wooden dowel rod, and some velcro cord straps:



      Normally these are used to wrap and contain electrical cords – e.g. inside your house. Not sure how they will stand up to outdoor weather. But I was able to fix the hose and keep it flat and level. We will see how it holds up.

      (edit: Corrected bad wording. The important part of setup is not “make sure the connector hose is level”, but rather: ensure the connector hose attaches to the downspout at a level *lower* than the highest water mark / highest water line of the rain barrel itself. This is what makes the water stop filling the barrel, and begin to backflow into the downspout, continuing on its journey. Thank you to community member Robert Larson for the questions and help identifying this incorrect phrasing.)

      • 2

        Amazing project! You did a great job at building it and showing us how it’s done.

        My first thought would be that the hose from the gutter to the tank would have to be on a downward slope so the water takes the path of least resistance but you are saying it should be as level as possible. Is that because that once the tank fills up the excess will just go down the gutter as normal?

      • 3

        Hello Robert, thank you for the kind words.

        >as level as possible. Is that because that once the tank fills up the excess will just go down the gutter as normal?

        Yes, exactly as you say. This is not my personal advice but rather the instructions from the manufacturer. If the connector hose is level, then once the rain barrel is full of water the connector hose will fill up also. Then any rain coming down the downspout will be ‘pushed’ back and unable to enter the connection hose. This will cause it to simply continue down the spout and out the gutter system normally.

        Here is a picture from the manufacturer instructions showing “too low”, “too high”, and “acceptably level”.

        attachment height

        To me the ‘correct’ diagram appears to still angle slightly upward.
        I believe the important bit is to connect to the downspout below the highest water level in the barrel. The instructions emphasize several times to install the diverter below the highest water line.

      • 2

        Those diagrams make it very clear, thanks!

      • 3

        Hello Robert – Your comment has helped me to realize that I have been using very incorrect wording in this description.
        Above I was using the wording “make sure the connector hose is level”.
        However – this is not correct.
        The actual goal is to make sure the connector hose is *below the highest water level* of the barrel.
        This is the important part.

        As you have noted and can see from the diagram – it does not matter so much if the connection hose is exactly level or flat.
        What matters is that the hole in the downspout is *lower* than the highest water line inside the water barrel itself.
        This is obviously what makes the water stop filling the barrel, and begin to backflow into the downspout, continuing on its journey.

        All through my writing this post, I was mentally treating these as equivalent.
        Stating “below the highest water line” is what I _meant_ to convey.
        But clearly here I have used the wrong wording.

        I will go back and edit these posts to correct this. I hope that the change makes things more clear.

        So thank you very much for your comment and question; they have helped me to recognize this mistake, which is a quite central point and critical part of the setup.
        Thank you!

      • 2

        Great follow up reporting. Makes sense on how you explain attaching the hose, good clarification. I like the dowel idea, I probably would have tried to attach it to the building which likely wouldn’t have been ideal. 

        I have this installation kit, the barn gutters finally got put on last week, now I need to do this!