BuildingIrrigationWater ConservationWater Harvesting

Come On Out, The Water’s Fine: Rob Talks Rain Tanks!

by Rob Avis, Verge Permaculture


Hey everyone. I just shot a short video on setting up a low-tech rainwater harvesting system that can be employed for an urban yard. The tank that I used is typically used for shipping food all over the world. Some might say it is indigenous to the planet. While the volume of these tanks are relatively small, they work for small irrigation projects like our salad greens bed.

In addition to the video, I have a drawing below that details all of the components of a rainwater harvesting system. Feel free to place your questions below if you have any.

Anatomy of a rain tank
Click for larger view


  1. Good design except for the heavy stuff that gathers at the bottom, there’s no easy way to clean it up.

  2. Thanks! I have a set up right now with 3 55gal barrels. It fills with 1 inch of rain. This week we had over 6 inches of rain.

  3. Yes indeed, there should be a drain at the really bottom for flushing the stuff that has accumulated. IBC containers seem to be convex on top and flat on bottom. I don’t know if the metallic structure allows it, but what about flipping it over and installing a drain plug right where the last water would be converging ?

    Apart of that great design.

    Specially designed water harvesting elements are hard to come by as soon as you step out of North america or Australia. It is thus important also to mention that one can build first flush and complete water harvesting systems out of commonly found piping elements or even scrap material… We held a rain water harvesting workshop in Japan and used for instance a PET bottle instead of a ball, as it fit perfectly in the pipe.

  4. Nice one Rob, what is your rainfall there? The principles of your set up are basically the same as we commonly have in Australia, but for those of us with a much lower rainfall we have to reverse the seasonal activity.
    Our tanks don’t freeze (cool climate, not cold climate) so the priority is to store the winter water.
    Then in summer most rainfall events are small and therefore all they do is wash the dust, bird poo and debris off the roof into the tank, so that is the time to divert this heavily organic contaminated(nutrient rich)water into swales to support plant growth, particularly in the driest time of the year.
    I wouldn’t be too worried about the tank growing a small amount of algae, it actually helps clean the water (hope this helps Paulo) and it is important particularly with making it safe to drink that you place the outlet about 10cm at least above the tank base, you aim to keep that anaerobic sludge still.
    And for anyone worried about the water being too contaminated to drink because of heavy metal/pollution contamination just remember that if it is in the rain and on your roof then it is everywhere in the atmosphere around you so you might have to stop breathing as well as drinking.
    Slightly contaminated tank water is far better for you than the carcinogenic rich, municipal treated garbage served up as safe drinking water all over the first world in particular.

  5. Nice article. Seriously, some of you people who focused on the collected gunk at the bottom of the tank need to think BIG. I’m really big picture.

    Are you aware that even large scale public dams silt up and accumulate organic detritus at the bottom? I remember from the last serious drought here that the bottom 12% to 13% of reservoirs (dams for drinking water) was considered dead water. These were in closed catchments too (ie. no development) surrounded by healthy forests in Melbourne’s water supply regions.

    I drink rainwater and have 100,000 litres stored here and can assure you that town water produces more biological gunk when stored than the rain water ever does. I do not run a first flush device either, but I do live in a rural area which helps reduce contaminants.

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