Decentralized Water Reuse

In consideration of trends such as urbanization (faster than centralized infrastructure can effectively accommodate), energy use, and climate change/resilience, we begin focusing on decentralized water reuse.

Are there prime examples for small-scale/community scale, modular, decentralized water reuse systems? And are there such systems that treat wastewater to potable quality and are energy efficient?

If you share decentralized examples, it would be immensely helpful if you can share details as:

  • The Input (wastewater? industrial water? both?)
  • The output (to what quality are they treating the water?)
  • The source (i.e., the grid or maybe it’s mobile?)
  • How large are the systems in sq/m or sq/ft
  • What happens to sludge and effluent water?
  • How much water is processed (volume) or how many users it can serve?

@Vero, @rdrogers, do you know of any examples?

There were two people one at Berkeley and one at McGill doing things like this. I will see what I can find.

See article on water related to adapting to climate change: page 36 Chemical & Engineering News | CEN.ACS.ORG | FEBRUARY 10, 2020

@FECHINE, thank you for joining our online community!

I’d like to invite you to join this discussion. Our research team is looking for examples of small-scale, modular, decentralized water reuse systems. Are you aware of any?

I found the contacts with potential good examples:

New American Chemical Society journal on Water:

Thank you so much, @rdrogers! I’m going to see if I can invite Mulvihill and Basu to the community, and our researchers will check out those papers.

@Farzaneh64, @engrthakur, you might also have insight on @Eti’s question. Please let us know if you’re aware of any small-scale, modular, decentralized water reuse systems.

@Vesa, @gtparker, thank you for joining the community! We’d love to get your feedback on this topic.

I would like to share some of my thoughts with this community.
But first of all I would like to apologize in advance if I point out the obvious.
We are many who are concerned of the environment and who has been thinking of this subject.
Personally I have spent years thinking of inventions. New inventions are important but the environment needs help now.
So the logical solution for me is to point out examples of existing ideas worth to be spread.

  1. Orbital systems have a shower system influenced by NASA. It reduces water consumption about 90 % and energy about 80 %.
  2. Vacuum/pump toilet system with a very low use of water. The waste is collected in biogas chambers or composting tanks. The gas can be used for cars, heating, eventually cooking etcetera. It is good if it is possible to extracting elements from the remains. And if you can clean the remains from medicines it is suitable to use as a compost to make soil. Otherwise it is suitable to burn and make use of the energy.
  3. The remaining gray water has been reduced by following the ideas above. The remaining can be filtrated by sand filters if necessary and be used for an example watering the grass and garden.
  4. It is possible to make artificial ponds and make areas where you dig out existing soil and replace it with for an example sand or preferably rock flour due to the fact that sand is a limited resource in many parts of the world. This makes it is possible to harvest and store rainwater locally. Filter the water accordingly to the need.
  5. By following these quite easy steps we can reduce the use per person in the west from around 100-160 l per day to actually in practice zero. And in best case scenario to be a producer. We can also reduce or eliminate the harmful waste from WC systems and can make biogas energy or soil instead.
    This was just a few examples.
    I totally agree with the opinion that what we call waste and problem is a resource and a necessity to reuse.

Vesa Lius

@Vesa Thank you so much for this wonderful insights! These are in fact new to the community and very interesting – do you have some links to share so we can read a little more on these subjects? particularly around orbital systems would be extremely helpful.

It’s a late Friday, but let’s have a go. Can I gently suggest the problem is sort of scoped wrong? Or perhaps not really scoped at all?

My understanding is that some water on the space shuttle is recycled from wastewater to drinking water. Similarly It’s worth pointing out that UV treatment is free if you have enough space. But most people don’t.

Context is everything. EVERYTHING.

Energy efficient is relative. And maybe misses the point? If the energy is solar and a huge portion of it is reflected back into space, efficiency per se is maybe not the metric to use? Alternatively, at some latitudes there is a much more finite resource there.

It’s also worth pointing out that conventions/shorthand like ‘sludge’ also perhaps miss the point. Struvite was a nuisance. Guano is mined. It is more or less the same stuff.


I should also say that I had a student a few years back do something like a gap analysis which evaluated e.g. cost vs. efficacy of treatment vs. treatment scale (very important for decentralised systems)

It turns out there are clear winners in some parts of this space and then there is a space with no winners and/or no appropriate solutions.

The things that the OP definitely gets right I think are that quality of water is a sliding scale (this is not that dissimilar from well-accepted paradigms e.g. oil and refineries/distillation). The NEW Singapore system might be a relevant reference point here for water.

The thing about oil/gas paradigms though is that there is a narrow criteria which is, briefly, energy content (when it’s burned) per kg.

I see somewhat less value in the coarse colour systems blue/green/grey/black that are often used for water.

There is a long history of people getting this quite wrong. Saying water is ‘Blue’ is of limited use if you then discover that the same water might be really really harmful (even lethal).

Thank you for your kind response.


I hope the links work.
An example of a small biofilter for gray water

The importance of rain water harvesting

The rain is irregular in many parts of the world.
Long dry periods followed by sometimes rather intense rain.
This causes the water to flow down to the seas or evaporate without doing any good.
Often, the rainfall also takes away existing good soils.
Now innovative people in, for example, India East Africa and Australia have started taking wise steps to use the water. Some examples are by conducting the water to artificial and natural ponds.
By studying the terrain and taking action in the right places, by barriers, to collect water in sandy layers and wells both new and renovated.
The groundwater can also be replenished via wells etc.
In Australia, successful attempts have been made to adequately curb small rivers to create ponds.
The water continues to flow after the pond.
They are prominent in reclaiming desert areas in China.
Among other things they have a method to change the soil structure.
Combining these methods should lead to success.
On a smaller scale, as I wrote earlier it is appropriate to collect water in cisterns with circulating water to sand layers or to artificial ponds.
The cisterns should preferably be in the ground as they maintain a more even temperature thanks to the soil.
Above ground it can be very hot which can lead to unnecessary evaporation and the risk of bacterial growth increases.
The water can be purified both before introduction to the cisterns in the cisterns through circulation and natural oxygenation after the cisterns, the water is led through a suitably adapted filter system.

One example.

An example
San Diego California.
There is not much rainfall in San Diego. The annual average burden is 266 mm.
A homeowner has a roof of a total of 200 m2.
1 m2 and 1 mm of rain provide 1 liter of water.
200 m2 and 266 mm provide approximately 53,000 l of water per year.
By harvesting water according to previous proposals, the supplementary need per person should be able to be reduced to 30 l per day. If there are 4 people living in the house, the annual need becomes 4x30x365, i.e. about 44,000 l.
That is about 9000 in surplus. Some of the surplus is evaporated, but according to the calculation example there is the possibility of getting sufficient quantities for the household.
The gray water that is off to poor quality from showers washing machines dishwashers etcetera to be re-use directly is probably in sufficient quantity to suffice water the lawn garden etcetera like I suggested earlier.
If the climate is even drier, the water-collecting surface can be increased and in real extreme cases it may be necessary to add small water from the air system.
If it is one of the AC model, it is optimal to only run it at night when the air is cooler and thus relatively humid, less energy is needed.