The water footprint of a product is an environmental indicator that represents the total amount of fresh water used throughout its life cycle. That is, from the production of raw materials to their final consumption, as well as the management of the waste generated throughout that cycle.
In the case of cars, this metric varies, in addition to the use of the car, depending on the type of energy source they use. The production of fossil fuels does not require the same amount of water as the generation of electricity or biofuels.
When talking about water footprint, it must be taken into account that it can be analyzed from two approaches: consumption and water use. The first refers to fresh water that is completely consumed to carry out the activity or process. The second refers to fresh water used but which, after use, is returned to the hydrological cycle.
When studying the water footprint of passenger vehicles, it seems more appropriate to focus on a water consumption approach. This takes place both in the life cycle of the energy source (specifically in the production stage) and in the life cycle of the vehicle (manufacturing, maintenance and management at the end of the useful life of the vehicle itself and each of its components). components).
To analyze the water footprint of different types of cars, we have selected a set of 16 scientific articles published since 2015 based on a bibliographic review (not previously published). The results of the work reveal some evidence.
In internal combustion vehicles, 70-80% of water resource consumption comes from the production of the energy source. The vehicle life cycle represents the remaining 20-30%. In the case of battery electric vehicles, this distribution does not change substantially, with the production of the energy source (electricity) also being the main contribution to the consumption of the resource.
According to some results collected, the plug-in hybrid vehicle could increase the water footprint between 27 and 77% compared to the internal combustion vehicle. This increase is directly related to how electrical energy is generated to recharge the batteries of these cars.
Thus, for example, generation via hydraulics or using biomass as a primary energy source has greater water consumption, while if it is obtained from wind energy the impact is reduced.
For the same reason, the electric vehicle could increase the water footprint between 96 and 186% compared to the combustion vehicle.
Taking bibliographic data on the water footprint of the different sources of electricity generation, the European electricity generation mix in 2022 and the average consumption of an average electric vehicle sold in Europe in that same year, it can be determined that the contribution From the production phase of the energy source of the electric vehicle to the total water footprint amounts to 90%.
For the fuel cell vehicle that runs on hydrogen, water consumption can increase by 147-1178%. These values depend on the hydrogen production process and the raw material used for this purpose.
For example, it is estimated that the production of hydrogen from biomass gasification practically fivefolds the water footprint of hydrogen from natural gas and water electrolysis. In the latter case, that of electrolysis, and due to the consumption of electricity in the process, the environmental impact is also completely determined by how the electrical energy is generated, just as in electric vehicles.
Thus, the fuel cell vehicle with hydrogen from the gasification of biomass would increase the water footprint by more than 1,000% compared to the combustion vehicle. If the hydrogen comes from natural gas, 147%. Finally, if it comes from the electrolysis of water, it will depend, as mentioned, on how the electrical energy is generated: if it is via wind, the impact will be less.
If the use of biofuels in combustion vehicles is considered, notable differences are observed in their impacts on the water footprint. Bioethanol, biodiesel (methyl esters of fatty acids) and hydrogenated vegetable oil have a larger water footprint than the fossil fuels used in the same internal combustion engines.
These increases will depend on the raw material used for the process of obtaining the biofuel. In the case of biodiesel and hydrogenated vegetable oil, the water footprint could increase up to 4-8 times. In the case of bioethanol, and due to the high water requirements of the starting crops, the increases could reach several orders of magnitude.
The consumption of water resources from these energy sources is significantly reduced if the starting raw materials were waste (secondary raw materials). In this case, environmental burdens associated with the management of this waste may even be avoided.
Given all this data, it must be taken into account that the consumption of water resources is one more environmental impact of cars, as are the carbon footprint and other relevant impacts.
Choosing a specific technology and energy source may reduce some impacts and increase others, but there are no single solutions that reduce all of them or eliminate them completely.
This article was originally published on The Conversation.
Javier Pérez Rodríguez is a professor at the Department of Industrial and Environmental Chemical Engineering, and a member of the Environmental Technologies and Industrial Resources Group, Polytechnic University of Madrid (UPM), in collaboration with Adriana Affili, student at the Higher Technical School of Industrial Engineers from the Polytechnic University of Madrid.
