In the previous publication, we discussed water consumption in hydrogen production and its importance in this type of facility. Below, we’ll take a closer look at the most relevant technical aspects that influence a plant’s water consumption. The aim is to answer several key questions that may arise when developing a hydrogen production project, such as:
How much water is needed to produce hydrogen?
What water sources can be used?
What is the procedure for securing water access at the facility?
What level of water purity is required for hydrogen production? And for cooling systems?
Can water be recycled in the hydrogen production process?
How can water consumption be minimised?
Etc.
Context
As mentioned in the previous article, the most significant sources of water consumption in hydrogen production come from electrolysis and process cooling. Illustration 1, for instance, can give us an idea of the water requirements of such facilities. As an initial estimate, a plant producing 10,000 tonnes of hydrogen per year could require around 350,000 m³/year of untreated network water.
To begin with, it is particularly important to understand the differences between the various types of water involved in the hydrogen production process. The main distinction between them lies in water quality, as the requirements vary depending on which part of the process the water is used in.
- Untreated network water: this refers to the incoming water supplied to the facility, which must be treated to achieve the required level of purity depending on its intended application.
- Ultrapure water: water that meets the quality requirements of electrolysers. But what level of water quality is actually required in electrolysers? Well, that depends on the specific technology used, as we’ll see in the next section.
- Cooling water: used in the cooling process to dissipate heat from production operations and help maintain the temperatures targeted under the operating conditions. It is considered an auxiliary service with its own specific quality requirements.
- Reject water: this is the outflow from the water treatment plant, where network water is treated to produce ultrapure water. As a result of this process, a reject stream with a higher concentration of impurities is generated, which is typically purged from the system.
Illustration 1. Water requirements across the different stages of hydrogen production. Source: IRENA (2023).
In the case of cooling—just as with electrolysis—electricity and water consumption vary depending on the technology used. As we’ll see below, the most common cooling technologies used in production plants include cooling towers, dry air cooling systems, and adiabatic systems.
The amount of water required depends on the plant design, the type of electrolyser, the water treatment system, and the cooling system. This will affect the quantities of ultrapure water needed, as well as the associated raw water, and—due to the cost of water treatment—the overall cost of the plant.
From an administrative perspective, it is necessary for the relevant river basin authority to process the permit for the use of that volume of water at the facility. This is a key aspect of the permitting process for hydrogen production projects.
At AtlantHy, we view water consumption as a critical factor in the viability of hydrogen projects—one that must be considered from the very outset. And why is water consumption so important in hydrogen plants? In Spain, there are various regions affected by water stress, which may struggle to meet increased water demand effectively (Illustration 2). One of the key objectives when designing a hydrogen production plant is to minimise its water consumption and reduce the impact the project may have on local water bodies.
Illustration 2. Water scarcity situation in Spain, August 2024. Source: Subdirectorate-General for Water Planning, 2024.
Water consumption in electrolysis
For hydrogen production, based on the stoichiometry of the reaction, the previously mentioned 9–10 litres of ultrapure water are required per kg of H₂. However, in practice, this translates to around 15–16 litres of network water per kg of H₂.
The quality of water required for use in electrolysers is determined by each technology provider and is specified to maximise both efficiency and the service life of the equipment. This value is set sufficiently low—particularly in terms of electrical conductivity—to ensure that the concentration of harmful ions and molecules remains below the limits tolerated by the electrolyser. Typically, the water must meet ASTM Type I standards for PEM technology and Type II standards for alkaline technology (Table 1).
Table 1. Main water purity requirements according to ASTM Type I and II standards. Source: ASTM (2023)
| Resistivity (MΩ-cm) | Conductivity (μS/cm) | pH 25˚C | TOC (μg/L) | Sodium (μg/L) | Chloride (μg/L) | Silica (μg/L) | |
| Type I | > 18 | < 0.056 | N/A | < 50 | < 1 | < 1 | < 3 |
| Type II | > 1 | < 1 | N/A | < 200 | < 5 | < 5 | < 3 |
In alkaline technology, the water circuit in the process involves the addition of water and its mixing with the electrolyte used. PEM technology, on the other hand, is generally associated with higher water consumption than alkaline systems. For the same amount of ultrapure water, the required volume of raw water will vary depending on the electrolyser technology used.
At this stage, it would involve oversizing the capacity of the water treatment plant—something that would lead to an increase in both the CAPEX and OPEX of the project.
Water consumption in cooling
Cooling is an auxiliary service within the facility, and given the large amounts of heat that must be dissipated, it becomes a factor that significantly affects overall consumption, depending on the technology used.
The choice between the most common cooling technologies for hydrogen production plants will depend on each specific case. The main characteristics of each are summarised in Table 2 in relation to water consumption, and it is important to note that these are approximate reference values. Significant variations may occur depending on the climate conditions of the plant’s location.
Dry cooling systems (dry coolers) are those that minimise water consumption to the greatest extent, but they also have the highest electricity demand. However, in climates where temperatures are high during part of the year—such as in Andalusia—these systems may not have sufficient capacity to meet cooling demands.
In such cases, it is appropriate to install systems that use water to take advantage of its temperature difference and latent heat of evaporation to cool the process fluid. Cooling towers are systems that consume water continuously, whereas adiabatic systems are more similar to dry coolers and operate dry until water needs to be added to the system to meet the cooling demand.
For this reason, adiabatic systems have a lower annual water consumption than cooling towers, although they also require a larger footprint within the plant to deliver the same cooling capacity.
Table 2. General characteristics of the different types of cooling technologies.
| Cooling tower | Dry cooling | Adiabatic systems | |
| Water consumption (m3/t H2) | 50 | 0 | 10 |
| Required space (m2) | Low | High | High |
| Water purity | Network water or equivalent | N/A | Demineralised water |
Looking at the table, it is worth highlighting that cooling towers can be designed and fitted with packing material that allows for the use of lower-quality water, including treated wastewater. This presents an option worth exploring, as it can lead to reduced network water consumption and contribute to the enhanced integration of circular economy principles.
In general, the hydrogen production industry is mostly opting for dry coolers where the climate allows, and adiabatic systems in other cases. In future articles, we’ll explore in more detail the choice of cooling systems and the characteristics of each technology.
Water purification systems
Once the different water purity requirements within a hydrogen production plant are well understood, we can now review how to obtain ultrapure water from mains water. If river water or seawater is used, additional treatment systems would be required to first meet network water quality standards, in line with the criteria established in Real Decreto 3/2023 of 10 January, which sets out the technical and health requirements for the quality, control and supply of drinking water. To meet these standards, some of the systems that could be implemented include DAF (dissolved air flotation) systems, biological treatment systems, and ultrafiltration.
Illustration 3. Water treatment system for a hydrogen plant.
To treat mains water and obtain ultrapure water, the optimal technology typically involves the use of double-pass reverse osmosis systems for the removal of ions and organic matter (see Table 1). This process involves two stages, each equipped with a semi-permeable membrane. On one side, high-purity water is obtained, while on the other side, the permeate is produced—a water stream containing the contaminants retained by the membrane.
Even so, it is still necessary to reduce electrical conductivity, which can be achieved using electrodeionisation (EDI)—a filtration process that uses ion exchange resins subjected to positive and negative voltage. The EDI system uses electrical energy to reduce the ionic load of the water.
Water abstraction licence
Let’s now consider the case where the project has already been designed and the expected water consumption of the hydrogen production plant is known. At this point, it is necessary to carry out the corresponding administrative procedure in order to obtain the water use permit.
For industrial plants, given the high flow rates involved, a water abstraction licence for private use must be obtained, following the procedure outlined in Illustration 4, which may take up to 18 months to be processed.
Illustration 4. General procedure for obtaining a water abstraction licence for private use. Source: Ministerio para la Transición Ecológica y el Reto Demográfico (n.d.).
The application must be submitted to the corresponding confederación hidrográfica (River Basin Authority). These authorities generally have their own Plan Hidrológico (Hydrological Plan), but in general terms, their priority for granting water abstraction licences for different uses is as follows (Subdirección General de Dominio Público Hidráulico e Infraestructuras, n.d.):
- Public water supply, including the necessary allocation for low water-consuming industries located within population centres and connected to the municipal network.
- Irrigation and agricultural uses.
- Industrial uses for electricity generation.
- Other industrial uses not included in the above categories.
- Aquaculture.
- Recreational uses.
- Navigation and water transport.
- Other uses.
In general, to submit this application, the following information must be provided to the competent authorities: the applicant (titleholder), the intended purpose of the use, the duration of the licence, the maximum instantaneous flow rate, the maximum annual volume, and, where applicable, the maximum monthly volume to be authorised, specifying the period of use if it is to take place on restricted days.
Conclusions
Water consumption is an important consideration in any hydrogen project and can influence the overall viability of a hydrogen production plant. This consumption may vary depending on the type of electrolyser and the cooling system used, with dry coolers and adiabatic systems generally requiring less water.
It is also essential, during the early stages of the project, to begin the procedures for applying for the water abstraction licence for private use, which is critical to ensure the project can be carried out.
If you want to learn more about water treatment, don’t hesitate to listen to our Episode 76 with Sergio Meana from Hidritec.
At AtlantHy, we can support both the design of the facilities and the application for the water abstraction licence before the relevant river basin authorities. We assist projects in selecting appropriate technologies—both for electrolysis and cooling—including carbon capture and synthetic fuel production plants. We also help conceptualise the project to ensure all necessary environmental procedures and approvals are successfully completed.
Bibliography
ASTM. (20 de 03 de 2023). American Society for Testing and Materials. Retrieved from https://www.astm.org/d1193-99e01.html
IRENA. (2023). Water for hydrogen production. Retrieved from https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2023/Dec/IRENA_Bluerisk_Water_for_hydrogen_production_2023.pdf
Ministerio para la Transición Ecológica y el Reto Demográfico. (s.f.). Concesiones para el uso privativo del agua. Retrieved from https://www.miteco.gob.es/es/agua/temas/concesiones-y-autorizaciones/regulacion-usos-aprovechamiento/concesiones.html
Subdirección General de Dominio Público Hidráulico e Infraestructuras. (s.f.). Concesiones en la legislación de aguas. Retrieved from https://www.miteco.gob.es/content/dam/miteco/es/agua/temas/concesiones-y-autorizaciones/procedimiento-ordinario-otorgamiento-de-concesiones_tcm30-509087.pdf
Subdirección general de Planificación Hidrológica. (septiembre de 2024). Informe mensual de seguimiento de la situación de Sequía y Escasez. Retrieved from https://www.miteco.gob.es/content/dam/miteco/es/agua/temas/observatorio-nacional-de-la-sequia/2409-Informe_SE_sep_2024.pdf