Low cost multi-mode passive water harvesting and filtration system



Challenge Addressed:
Cape Town uses about 300-million cubic metres of water per year, and on average, around 4x that amount (1200 million cubic metres) falls on the city each year as rain. Current affordable rain harvesting solutions such as Jojo tanks do not provide sufficient water supply storage to last more than a few weeks. Water cisterns that can supply an average family for a practical period of time are too expensive, even for middle class families. If we can find low cost method to create effective water batteries at different scales, we can improve water resiliency for homes and community scale.

Proposed Solution:
A low cost water cistern built using ferro-cement, traditional earth construction techniques, or 3D printing that can store tens or hundreds of thousands of litre of water, coupled with modular, multiple modes of passive water harvesting including rain, fog and subterranean condensation, with use determined by climate and geological conditions.The cistern also has a passive filtration section that filters water for potable water use.

Desired Hackathon Goal:
1 Literature review
2. Determine economic feasibility
3. Explore design alternatives
4. Design modularity and standard permutations for different climate and application scenarios

Resources Needed:

  • water purification researcher or engineer
  • mechanical engineer
  • cement or building scale 3D printing technologist
  • maker
  • Industrial designer with 3D CAD experience.


Hi there, this new technology may be of interest too - http://the-awe.com/


That’s an awesome concept! Actually my colleague Markus and I first thought about turning wind energy into compressed air for the open source circular designed ecohome my wife and I are building. That avoids the expensive electrical components. But I never thought about the idea that it could also generate a lot of water at the same time!

We are thinking of a multimodal water harvester so we could integrate all kinds of tech into it. fog nets and condensation pipes are other add on modules. They can be applicable in regions where the climate conditions make it feasible. Also, another add on module can be a gray water cistern and low cost solar still. We’ll be using HUMAN CAD to draw different potential architectures! Some industrial designers who join may want to go beyond human cad though…

The more cool tech we can bring into the commons, the less we have of monopoly patents that restrict ideas from flowing to the people who need it the most.


Wow it would be great if someone wise or knowledgeable could assess the utility of possibilities. I’ve just remembered I’ve collected another couple more here -



Wow! Lots to think about from that one. Storage is a big issue and compressed air is pretty easy to move about - interesting.
I’ve always like the Savonius wind turbine - basically an oil drum cut in half and stuck on a pole.


Hi Gien,
Was thinking about the home you are building.
We manufacture bricks (full, construction-grade, cinderblock-sized ones) from plastic waste!
Thought it may be an interesting addition to the structure and eco-friendliness of your home.

If you are interested, I will be at the hackathon, but haven’t submitted an idea, as I’d like to experience it and maybe add insights to a team or two first.

Anyway, see you at the hackathon!
Warm regards,
Theo (079 798 8558)


I really like the intention of this project, but it is very light on verifiable claims about cost, availability and output.


Hey Theo, did I get to meet you? So many people I can’t remember if I met you or not. Did you see Dyllon’s talk? His research has found a way to make bricks out of urine! Are you coming on Sunday? We are going to get more into the hackathon tomorrow.


Hi Markus,

The core idea is to build low cost ferrocement water tanks for storage. There are many existing designs for these. Carrie, who was with Conway today, build a 25,000 Litre one…4 meters wide, 1.5 meter tall. quite rapidly and with low cost…it’s just labor intensive.

UN has a guidebook and has been building across Africa for decades.

Could create a tank and, where there are no rooftops can apply biomimicry to open the collection leaves like a flower petal opening:

to magnify the capture amount.


Here’s some design sketches of the water tank. They are part of a NEXUS approach combining water with food



Hey Michael (@MPThompson) and Jerome, what do you think of these designs?


i know is a different technology but have some similar concepts.



Hey Ricardo! Yes, I’ve seen that one. I name it multi-modal passive because it includes the fog net and underground condensation options as well. But as Markus noted, it will be determined by the local whether conditions. Rain will typically give you your highest volume of water in tropical and Mediterranean climates but not in arid ones. There, subterranean condensation pipes may be more effective. In fog rich climates, fog nets would be appropriate. Where I live, we have rain and fog, but the subterranian condensation pipes don’t work well.

So if we are taking a global approach, we need to create a map to look at humidity, temp, rainfall patterns, soil to calculate a profile to determine efficiency of each type of passive water harvesting.