Industrial water reuse: strategies, technologies and regulation

Industrial water reuse means treating a plant's wastewater so it can be used again for new purposes instead of being discharged. That additional treatment, called regeneration, turns treated effluent into reclaimed water with the quality each application requires: from irrigating green areas to feeding cooling towers or manufacturing processes.

For industry, reuse is no longer a marginal option. Against a backdrop of water scarcity and rising water stress, reusing water cuts fresh-resource abstraction, brings supply security and fits squarely into the circular water economy.

What industrial water reuse is

Water reuse or reclamation is the use of treated wastewater for new purposes, rather than discharging it to the environment. Before it can be reused it needs regeneration: an additional, usually tertiary or advanced, treatment that brings the treated effluent up to the quality the intended use requires.

It helps to distinguish three concepts that are sometimes mixed up:

• Treated effluent: wastewater that has been through a treatment plant (secondary treatment) and meets discharge limits, but not necessarily reuse limits.
• Reclaimed water: treated effluent that receives an additional treatment to reach the quality a specific use demands.
• Reuse: the act of using that reclaimed water in a new application, whether inside or outside the plant.

In industry, much of the reuse is internal: the factory regenerates its own effluent and puts it back into its processes, closing the loop and cutting both abstraction and discharge. It is one of the most effective levers for lowering a site's blue water footprint.

Regeneration technologies for industrial reuse

There is no single reuse technology, but a combination of stages chained together according to the starting quality of the effluent and the target quality sought. The typical sequence starts from secondary effluent and adds membrane filtration, desalination and disinfection.

Tertiary treatment

This is the first layer of regeneration over the already-treated effluent. It combines filtration (for example sand or membrane filters) and disinfection to remove suspended solids, turbidity and micro-organisms. It is often enough for uses with moderate requirements, such as irrigation or certain cleaning tasks.

Membrane bioreactors (MBR)

Membrane bioreactors, or MBR, combine biological treatment and membrane filtration in a single stage. They produce very good quality water without conventional clarifiers and take up less space. They are common when the aim is to regenerate water directly for reuse with a small plant footprint.

Ultrafiltration and reverse osmosis

Ultrafiltration (UF) retains fine particles, colloids, bacteria and viruses, and often acts as pre-treatment. Reverse osmosis (RO) goes further: it desalinates and demineralises water, retaining dissolved salts, micropollutants and pathogens. RO shares its principle with seawater desalination and is the stage that reaches the highest purity levels, though it is energy-intensive.

Final disinfection and polishing

To guarantee sanitary safety, a disinfection step using ultraviolet (UV) light or ozone inactivates pathogens without leaving residues. Where dissolved organic contaminants are present, activated carbon helps remove them. The highest-purity water, after reverse osmosis, can feed cooling towers, boilers or demanding processes.

A typical industrial regeneration chain links these stages as follows:

The usual sequence is secondary effluent → UF or MBR → reverse osmosis → disinfection, adjusting stages to the final use. These solutions sit within the technologies to optimise the water footprint in industry.

Regulatory framework for water reuse

Reuse is regulated at both European and Spanish level, and the framework has been substantially renewed in recent years.

Regulation (EU) 2020/741

Regulation (EU) 2020/741, of 25 May 2020, on minimum requirements for water reuse, has applied since 26 June 2023. It sets minimum quality, monitoring and risk-management requirements for the use of reclaimed water in agricultural irrigation: it defines reclaimed-water quality classes and requires a risk-management plan and a permit to produce and supply it.

Royal Decree 1085/2024 in Spain

In Spain, Royal Decree 1085/2024, of 22 October, approving the Water Reuse Regulation and amending several royal decrees on water management, expressly repeals Royal Decree 1620/2007, which set the previous legal regime for reusing treated water. The new regulation:

• Expands and updates the catalogue of permitted uses of reclaimed water, listed in its Annex I.A, with new urban, agricultural and industrial applications.
• Regulates artificial aquifer recharge as an environmental destination for reclaimed water rather than a use: it follows a specific procedure, with the same quality requirements as other applications.
• Strengthens the quality criteria and the monitoring required of reclaimed water.
• Aligns with Regulation (EU) 2020/741, adopting the European risk-management approach.

Producing and supplying reclaimed water requires the corresponding authorisation or concession. In practice, this gives industry a clearer and broader framework to reuse water within its processes.

Benefits of reuse against water pressure

Reusing water goes beyond regulatory compliance: it is a water risk management strategy with concrete benefits.

• Less fresh-water abstraction: every cubic metre regenerated and reused is a cubic metre not withdrawn from the environment, which cuts the blue water footprint and pressure in stressed areas.
• Security and resilience: having an in-house source of reclaimed water brings water security and water resilience against droughts and supply restrictions.
• Less discharge and possible savings: putting water back into the process reduces the volume discharged and, in many cases, the costs tied to abstraction and discharge.
• ESG compliance and circularity: reuse supports circular water economy goals and improves performance in corporate water responsibility.

The main limits are cost and energy (reverse osmosis is electricity-intensive) and the quality required by each use, which determines which treatment stages are needed. Measuring the water footprint helps prioritise where reuse adds the most value.

Reuse examples by sector

Industrial reuse adapts to the quality each activity needs. Some qualitative examples:

• Food and beverage: process and cleaning water, with high sanitary requirements that usually call for membrane and disinfection stages.
• Textiles: dyeing and finishing generate effluents with a load of colour and chemicals; regenerating them allows water to be reused and discharge cut.
• Paper, chemicals and petrochemicals: high-consumption processes where internal reuse closes much of the loop.
• Energy: cooling water, a massive use that benefits from medium-to-high quality reclaimed water.
• Microelectronics: requires ultrapure water, with treatment chains that include reverse osmosis and polishing.

In most of these cases, internal reuse closes the loop within the plant itself. These measures fit with strategies to reduce a company's water footprint and with active management of the corporate water footprint.

Frequently asked questions

What is the difference between treated and reclaimed water?

Treated water has been through secondary treatment and meets discharge limits, but not always reuse limits. Reclaimed water is treated water that receives an additional treatment (regeneration) until it reaches the quality a specific use demands, and only then can it be reused.

Is it legal to reuse water in industry in Spain?

Yes. Royal Decree 1085/2024 approves the Water Reuse Regulation, expands the permitted uses, industrial ones included, and aligns with Regulation (EU) 2020/741. Producing and supplying reclaimed water requires an authorisation or concession.

Which technology is used to regenerate very high-quality water?

For the most demanding uses, ultrafiltration or membrane bioreactors are combined with reverse osmosis and a final UV or ozone disinfection. This chain removes salts, micropollutants and pathogens and can feed cooling towers, boilers or processes that need demineralised water.

Reduce your water footprint

With Manglai's water footprint software your company measures the water it uses, identifies where reuse genuinely cuts abstraction and the water deficit, and prioritises the regeneration investments that most strengthen your water security.