Location Middle East
As countries around the world set ambitious net zero energy commitments in order to avert the most catastrophic effects of climate change, it becomes crucial to focus on mitigating the carbon emissions of sectors that play a major role in everyday life and have correspondingly higher impacts on the environment. The water sector is one of those. Though many of us do not immediately associate water with carbon emissions, the process of extracting and transferring water for domestic or industrial use has significant embodied carbon. Such a predicament poses a real concern, as water remains the lifeline of any society and the demand for this resource continues to grow. In this article, Ibrahim Kronfol, the 2022 Vice President of the LEED Technical Advisory Group for Water Efficiency, discusses the hidden energy costs of water use and the focus of the water efficiency LEED unit for 2022.
Energy is embodied in the water we use, and it drives every part of the water use cycle: from extraction, through treatment and transfer, to discharge. Figure 1 shows the water use cycle as a cyclic multi-step process with two separate potable and sewage water streams. Each of the water transfer or treatment stages is associated with an average energy use bill, collectively adding up to a considerable energy consumption rate for every cubic metre of water we use.
Figure 1: Water use cycle – energy process.
In the very first step, water utilities extract water from an available water source: a river, pond, well, or even the sea. During this stage, energy is mainly consumed for pumping and can range between 0.05 and 0.2 kWh per cubic metre (kWh/m3) of water. In the next step, water is transferred to a treatment plant. Water treatment is the most energy-intensive step of the process, with requirements that range from 0.5 kWh/m3 for fresh water to 1.5 kWh/m3 for brackish water and an average of 3.5 kwh/m3 for sea water. When water achieves the level of quality it needs to qualify as potable water, it is ready to be transferred to cities and villages via a water conveyance process that will also consume 0.5-2.5 kWh/m3 and then to individual homes and buildings via a water distribution process that will charge another 0.25-0.5 kWh/m3. Even within the building itself, a further boost of 0.15-0.25 kWh/m3 is needed for the water to be ready for use.
In seconds, the potable water is consumed, and the same water begins a different journey back, in a wastewater stream that runs from the building itself to the water’s final destination, which could sometimes be the same source it came from. The wastewater stream’s first energy demand is associated with lifting the sewage that could not be drained by gravity, from within the building’s basement levels: this process consumes 0.05 to 0.2 kWh/m3 of energy. Sewage from buildings all over a given urban area will be collected and sent for treatment, a process that will mainly necessitate pumping stations and will consume another 0.05- 0.2 kWh/m3. At the waste treatment station, the sewage will pass through multiple filtration and purification processes requiring energy ranging from 0.3 to 0.8 kWh/m3 of energy depending on the technology. When it reaches its final destination, treated wastewater will be discharged back to the source or to a reuse facility, and even that discharge process will consume 0.05-0.2 kWh/m3. In brief, the total water use cycle will consume a considerable average of 4.5 kWh/m3.
Translating these figures into carbon emissions, we find that on average the water use cycle can emit 3 kg of carbon per m3 of water use. In other words, a single household could emit an average of 1 ton of CO2 annually, simply through the embodied carbon of the water it uses.
However, even these significant numbers do not tell the whole story, as they account only for water processing. In fact, the hidden bulk of energy consumed in the water sector comes from another source: heating water. As compared to the 4.5 kWh/m3 spent on average for water processing, water heating charges a staggering average energy bill of 58 kWh/m3. Correcting for hot water and assuming that 20% of water used in a household is heated first, the numbers would reach 10.4 kg of carbon per m3 and a single household would then be responsible for 4 tons of CO2 annually, as a result of its water use.
It is clear that these emissions need to be addressed in order for our societies to move to a net zero future. Mitigation acts start with end users: with each and every one of us taking effective actions to reduce and control water demand. Impactful awareness campaigns can help inspire people to do so, but it may require new policies and governmental legislative acts such as removing subsidies on water supplies – particularly on water use above the threshold required for decent living – that will help end users get a sense of the cost of the precious water and the energy required to deliver that water. Additional technical actions fall under the responsibility of the authorities, utilities and developers: these include setting targets to reduce leakage in distribution networks, implementing digital transformation for water utilities in order to enable smart management and optimisation on systems operation, and last but not least deploying new technologies and adopting efficient water distribution and treatment technologies such as, for example, water desalination via solar domes.
In the LEED Water Efficiency TAG, we are working to develop a number of LEED targets for water stewardship and resilience, particularly for the design, construction, and operation and maintenance industry. These include working to ensure that all projects contribute to net positive water use in their local watersheds and reducing the carbon footprint of water use. With humanity facing down global challenges such as the depletion of freshwater resources and climate change trends, these targets and strategies will become ever more important and ever more urgent.