Energy & Cost - Decentralized Potable Water Reuse

Taking a systems approach to the Global (fresh)Water Crisis, we aspire to incentivize a water reuse system that will also be energy efficient and potentially achieve net-zero targets.

Looking at present-day systems and innovations - can you please advise us on energy use for potable water reuse systems, both centralized and decentralized? Can you also indicate costs (to include water, energy, and waste)?

I found an interesting report by the California Sustainability Alliance. They have leveraged advisors from the public and private sectors to develop, test and deploy creative strategies to transform sectors with high energy efficiency potential. This is a study they produced by it’s Water-Energy Committee.

Starting on page 34 of the report they begin to detail some frameworks to determine Energy & Carbon benefits as well as a framework to estimate the energy and carbon values of displaced water supplies. Hope it’s helpful!

@staylor22, @bhaskarmv, @Elaine71, we’d love to get your input on this. We are designing a prize to incentivize the creation of community-scale and net-zero devices that optimize the safe and decentralized reclamation of water from the grid and natural water bodies. (More info here.) Your expertise would be hugely valuable to us!

Thank you @Eti @TerryMulligan and @NickOttens for getting us started on this very important question!

We are starting some preliminary research to unpack all the relevant elements here to try to grasp the main cost drivers of traditional water extraction and more specifically waste water reclamation when it comes to energy.

Also, how do these costs vary over different contexts such as geography, policy and regulation, etc.?

When considering the energy associated with reclaimed water, it is essential to make the proper comparison. Water reclamation must be considered relative to the alternative, which is to develop new water resources and transport and treat the water. This assumes that the resulting wastewater will be treated partially, so we are considering only the energy to further treat the water for its intended use. The concept of Fit-for-purpose water is also essential here. Not all water needs to meet drinking water standards. When viewed through this lens, water reclamation often significantly reduces energy (and costs).

@gdaigger Many thanks for your comment here too; I just responded to your insightful comment about cost on another thread, so I was hoping to focus here on the aspects you raise re energy and water quality.

With regards to “not all water needs to meet drinking water standards.” This is a question we’ve been considering (potable vs. non-potable) – we increasingly hear that the higher the quality is - the more use cases reused water will have, and thus usage can increase. In addition, examples such as the DPR facility in Texas, USA, treat water to a potable level that can be streamed back to freshwater pipes. With that in mind, if the decentralized system can treat water to different levels - wouldn’t that potentially increase costs due to infrastructure needed to ensure health & safety standards? Instead of, for example, a potable quality that allows using existing infrastructure?

With regards to energy, is it the case that there are some energy savings as we shifted from centralized facilities to small-scale, decentralized systems? Can these achieve Net Zero (across energy, waste, and water)?

In the areas most likely to be affected by poor water supply what is abundant is solar and often wind. I have some low technology ideas building on outline ideas I submitted to the community earlier, which will require adaptation in the field, and other ideas that are speculative. Will you tell me if there is going to be an innovations discussion.

@Chicno, @rgovind837, do you have any insight on these questions for us?

@NickOttens @Eti @TerryMulligan Wastewater contains nutrients, N and P, these are the key inputs for photosynthesis, so using photosynthesis to treat sewage is the best solution. Micro-algae are the best organism to grow in wastewater, this process may be called ‘Phyco-remediation’ .

A good presentation on algae for wastewater treatment by Prof Tryg Lundquist is available
See slide 5 for a summary of energy costs of wastewater treatment.

Unfortunately the micro-algae programs of US Govt is managed by Dept of Energy and not by EPA. So the focus has been on using algae for biofuel production and not for treatment of wastewater. As a result of this wrong policy, we neither have biofuel from algae nor economical wastewater treatment, with nutrient removal.

@bhaskarmv Thank you so much for including this slide deck. The information on energy is very helpful for getting a baseline energy consumption of treating water. Also, wow - what an interesting set of systems for nutrient reclamation, I know using photosynthesis is your expertise so thanks for sharing a slide with that information as well.

@mickwaza we are definitely going to be moving into innovation very soon! I’ll tag you when we start those discussions.


The Aquatic Species program was conducted by US DoE from 1978 to 1998, the Close Out Report is available on

Diatoms are mentioned 180 times and Wastewater 65 times.
All the research, upto 1998, on use of Wastewater to grow Algae are listed.

US DoE website on Algae

US DoE’s focus is on Carbon.
We need to change focus to Water, Nutrients and Oxygen.

@malkhadra, @Gregn5, @nanditabthakur11, I’d like to ask you to weigh in on this before we close out the discussion. Can you advise us on cost and energy use of reclaimed water systems, including compared to traditional freshwater extraction and wastewater treatment?

@NickOttens, it is little difficult to make a general statement about the cost of water reuse and reclaim, but we can compare the cost of water reuse against other alternative water supplies. If we are assessing some water supply project ( reclycled ) so it is very important to know that the basic difference between economic cost and financial accounting and their benefits. If the water authorities can not afford a project which can beneficial for a society so it will not get built without any extra financial support. But if some local or state agencies come forward to give some subsidies for this project so it can… According to a global report…"The metropolitan water district of Southern California has offered $ 250 per acre-foot subsidy for up to 25 years for local water development ". In this order reclaimed water is used for both portable and non portable uses, so there are so many factors to affect the cost of water reuse program. These includes many things like size and location of reclaimed water sources, treatment infrastructure, transmission, pumping,concentrate disposal, timing and storage and financial cost also.

Understanding the water-energy nexus is of key importance in order to achieve the human goal of sustainable resource management. Energy requirements for reclaimed and traditional systems differ on the basis of final water quality requirement. Reclaimed water systems do not have the end goal of making ‘potable’ water therefore they function on lesser energy requirements than traditional freshwater systems. Traditional technologies for freshwater extraction such as reverse osmosis desalination and disinfection used for ‘potable’ water are more energy intensive in nature. Therefore, reclaimed water systems can replace the traditional potable systems for irrigation purposes and industrial applications as they do not require potable water. It can also prove of significance importance not only in arid areas, but also in well-developed cities by helping in reducing carbon footprint.

Reverse osmosis is not the only one systema for potabilising and desalination aims.
The use of energy available and the cost is also important as well as wastewater producto fo this process. Any technology in the future should not only convert water to human being consum but think of how the process would be or not sustainable in time and in carbon footprint consequences.