Working out the energy intensity of different water processes has been a seemingly simple equation up until now.
Add up the energy bills of the water utilities – make sure they include energy use for transportation, pumping stations, and treatment plants. Add up the energy costs of desalination processes. Add up the energy costs of treating water for reuse.
Then compare them all to each other in kWh per cubic meter of water.
The result is what global water analysts have been citing for years:
- Seawater treatment is the most energy intensive;
- Wastewater reuse and wastewater treatment come in second and third;
- Groundwater and lake/river water are the least energy intensive and therefore most carbon friendly.
There is just one problem with this conclusion… it is no longer true!
Communities use and discharge water in a similar way to the natural water cycle. Energy must therefore be measured and compared on a total system basis not on an individual process basis.
It is essential we ensure the systems we compare are assessed under the same conditions.
For example: A centralised system providing water from a lake or river and disposing sewerage to the sea can only be compared to a local recycled wastewater system within the centralised system – not a decentralised local wastewater system.
That means we must:
- Include energy used to treat sewage not just to ocean outfall standards which are way below recycled water standards – but include energy used to treat sewage to the highest standards. This would then be a more accurate comparison of the energy use of a centralised system versus a decentralised system.
- Include the energy required to provide water security within the centralised system such as a desalinated supply or a pumped extraction from another water catchment or groundwater source. These water security measures are used regularly but appear to be omitted from many energy assessments of centralised systems.
Using this assessment, the order of energy intensity for each scheme would probably identify a different outcome to the energy water nexus.
So why are we continuing to recycle old assumptions about water infrastructure?
It’s time to examine the true water infrastructure costs and that means:
- Dealing with the water cycle not the unit processes
- Ensuring system comparisons are carried out under similar environmental, social and economic conditions.
- Providing justifications for assumptions not just using existing data that may have the wrong assumptions.
- Utilising these true costs to underpin credible arguments that will guide communities, industries, and global markets towards a valuable outcome.
We plan to highlight the urban water myths over the coming months and will be encouraging trusted organisations to provide accurate research and create a new set of representations on which we can rely.
Terry Leckie is one of Australia’s leading water industry experts and a passionate advocate of water reform, championing key changes to legislation and regulation.
Terry is also Founder and CEO of Water Factory Company, Australia’s first private water utility which is creating affordable and sustainable smart water networks. More of his blogs can be found at Water Spectator.