What are they?

A discharge is understood as the direct or indirect release of pollutants into water or the public water domain, regardless of the procedure or technique used.

Within the public water domain, discharges include both those made directly into inland waters and those made indirectly through collector networks, stormwater networks or other drainage systems. Certain releases into groundwater are also considered discharges. (BOE)

Discharges can alter the physical, chemical or biological characteristics of water and affect ecosystems, water uses and human health.

Their potential effects include:

1. Reduction of the oxygen available in water, making it difficult or impossible for aquatic organisms to survive.
2. Introduction of polluting or hazardous substances, some of which may be toxic, persistent or bioaccumulative, affecting aquatic organisms and, directly or indirectly, human health.
3. Excessive nutrient input, particularly nitrogen and phosphorus, which can promote algal growth and cause eutrophication.
4. Alteration of the physicochemical characteristics of water, such as pH, temperature, turbidity, salinity or the concentration of solids.
5. Groundwater contamination, particularly where infiltration or inadequately controlled discharges occur.
6. Generation of sludges and other contaminated materials during treatment and purification processes.

In inland waters, the direct or indirect discharge of wastewater and waste products liable to pollute water is generally prohibited unless the corresponding prior authorisation has been obtained. A discharge authorisation is intended to contribute to achieving the environmental objectives established for water bodies and must establish the conditions applicable to the discharge. (Ministry for Ecological Transition)

The authorisation and control of discharges depend on the receiving environment and on the distribution of powers between the competent authorities. In inter-community river basins, authorisation is generally granted by the relevant river basin authority. Discharges into sewerage networks are also subject to the regulations and conditions established by the authorities responsible for those networks.

Land-based discharges into the marine environment are subject to specific legislation and to the framework for marine environmental protection.

What can be done?

Workers and their representatives can play a role in preventing and reducing discharges. To do so, it is important to understand both the company's environmental obligations and the risks that discharge management, treatment and purification activities may pose to workers' health.

Find out about the company's discharges

We can request information about:

1. What discharges the company generates and in what quantities.
2. What substances and mixtures the wastewater contains or may contain.
3. Which production processes generate the discharges.
4. Where the discharges take place and where they are discharged.
5. Whether a discharge authorisation exists and what conditions it contains.
6. Which pollutant parameters must be monitored.
7. What emission limit values have been established.
8. What wastewater treatment facilities are available.
9. How measurement, sampling and monitoring are carried out.
10. What measures are in place to prevent accidental discharges.

The discharge declaration used in the authorisation procedure must include information on the activity causing the discharge, its location, the qualitative and quantitative characteristics of the discharge, and the treatment and disposal facilities, among other aspects. (BOE)

The discharge authorisation must establish, among other aspects, the origin of the wastewater, the location of the discharge point, the flow rate, emission limit values, treatment facilities and measurement and sampling systems. (BOE)

Monitor risks to workers' health

Discharge prevention and treatment also have an important occupational health dimension.

The risk assessment should cover tasks that may involve exposure to:

1. wastewater;
2. sludge and other materials generated by wastewater treatment;
3. chemicals present in wastewater;
4. chemicals used in treatment processes;
5. gases generated during wastewater treatment;
6. biological agents.

Wastewater may contain chemical pollutants and biological agents, and wastewater collection and treatment activities may result in occupational exposure to both types of agents. (INSST)

Particular attention should be paid to:

1. cleaning installations;
2. maintenance;
3. sampling;
4. removal and treatment of sludge;
5. clearing blocked pipes and conduits;
6. cleaning tanks and collectors;
7. work in wells and other confined spaces.

Hydrogen sulphide (H₂S) may be generated in wastewater treatment plants as a result of biological processes. During certain cleaning and maintenance activities, it may accumulate in confined spaces and constitute a serious inhalation hazard. These operations may also involve oxygen deficiency, the presence of biological agents and the risk of explosive atmospheres. (INSST)

Preventive measures should therefore address chemical and biological risks, hazardous atmospheres and the risks associated with work in confined spaces together.

Check compliance with environmental obligations

The company must comply with the conditions established by the applicable legislation and, where appropriate, by its discharge authorisation.

We can check that:

1. discharges are properly identified and characterised;
2. the appropriate authorisation has been obtained;
3. emission limit values are complied with;
4. the required monitoring is carried out;
5. wastewater treatment facilities operate properly;
6. appropriate measurement and sampling systems are in place;
7. required records and documentation are maintained;
8. non-compliances are investigated and corrected;
9. procedures are in place for dealing with accidental discharges.

It should not be assumed that all companies have a general obligation to submit an annual “discharge declaration”. The declaration forms part of the authorisation procedure in the cases provided for by the applicable regulations, while the specific monitoring, information and reporting obligations depend on the type of discharge, the authorisation and the applicable legislation. (Ministry for Ecological Transition)

Prevent and reduce discharges

The best strategy is to act at the source of pollution, avoiding or reducing the generation of discharges before relying on treatment.

We can propose:

1. eliminating processes that generate unnecessary discharges;
2. reducing water consumption;
3. modifying production processes to reduce the generation of contaminated wastewater;
4. separating different wastewater streams;
5. preventing hazardous substances from entering sewerage networks;
6. improving treatment systems;
7. preventing leaks and spills;
8. installing appropriate containment systems;
9. establishing procedures for dealing with accidental discharges;
10. replacing hazardous substances with less hazardous alternatives where technically feasible;
11. progressively reducing the quantity and hazardousness of pollutants discharged.

The Ministry for Ecological Transition expressly highlights the importance of addressing pollution sources at their origin in order to reduce the impact of activities on aquatic ecosystems. (Ministry for Ecological Transition)

Propose the substitution of hazardous substances

When a hazardous substance used by the company may enter wastewater, it should be assessed whether it can be eliminated or replaced with a less hazardous alternative.

Substitution can provide simultaneous benefits:

1. for workers' health;
2. for the environment;
3. for water quality;
4. by reducing waste and emissions;
5. by preventing accidents and spills.

ISTAS publications on the substitution of hazardous substances can be used as practical tools for developing such proposals.

Participate in the company's environmental prevention

Workers' representatives can:

1. request information on discharge authorisations;
2. understand their conditions and limits;
3. participate in monitoring preventive measures;
4. request information on non-compliances and accidental discharges;
5. make proposals to reduce or eliminate discharges;
6. propose the substitution of hazardous substances;
7. request information on wastewater treatment systems;
8. propose measures to reduce water consumption;
9. promote pollution prevention at source;
10. link environmental measures with occupational risk prevention.

The ISTAS Guide to Discharge Control and Management is particularly suited to this type of intervention. It can be used as a practical tool to identify sources of discharges, carry out monitoring and propose prevention and minimisation measures. ISTAS continues to include this publication among its resources. (ISTAS)

Guidance for action

The following publications can be used as supporting tools for workers' intervention.

ISTAS publications are retained as practical references even though they predate the current legislative framework. Any legislative references contained in them should always be checked against the legislation currently in force indicated in this section.

ISTAS publications:

1. Guide to Discharge Control and Management. ISTAS, 2005.
2. Company Environmental Obligations. Guide for Workers' Intervention. ISTAS, 2010.
3. Guide to the Substitution of Hazardous Substances in the Company. Practical Manual for Intervention. ISTAS.
4. Prevention of Chemical Risks in the Workplace. Guide for Intervention

Classification

The list of substances relevant to water pollution includes:

1. Priority substances and other pollutants subject to environmental quality standards.
2. Preferential substances and other specific pollutants covered by water quality legislation.
3. Substances and mixtures classified as hazardous to the aquatic environment under the CLP Regulation.
4. Persistent, bioaccumulative and toxic (PBT) substances and very persistent and very bioaccumulative (vPvB) substances, where applicable.
5. Substances with endocrine-disrupting properties, where applicable regulatory criteria exist.
6. Metals and their compounds.
7. Hydrocarbons and other organic pollutants.
8. 
   
9. Other pollutants subject to environmental quality standards or emission limit values.

Royal Decree 817/2015 establishes environmental quality standards for priority substances and other pollutants, as well as standards relating to preferential substances and specific pollutants in surface waters. Its consolidated text incorporates subsequent amendments, including the update published in January 2023. (BOE)

It is important to distinguish between:

Hazardous to the aquatic environment under CLP ≠ necessarily subject to a specific environmental quality standard.

Legislation

Inland waters and the public water domain

1. Royal Legislative Decree 1/2001 of 20 July, approving the consolidated text of the Water Act, in its current version. This is the basic national legislation governing the public water domain and water protection. The consolidated BOE text records its latest published update as 28 December 2023.
2. Royal Decree 849/1986 of 11 April, approving the Regulation of the Public Water Domain, in its current version. Chapter II specifically regulates discharge authorisations.
3. Royal Decree 665/2023 of 18 July, amending the Regulation of the Public Water Domain, among other regulations. It introduced significant changes concerning the authorisation, declaration, monitoring and conditions of discharges, including the regulation of emission limit values and monitoring systems.
4. Royal Decree 817/2015 of 11 September, establishing the criteria for monitoring and assessing the status of surface waters and environmental quality standards, in its current version.
5. Royal Decree 1514/2009 of 2 October, regulating the protection of groundwater against pollution and deterioration, in its current version.

Urban wastewater

1. Royal Decree-Law 11/1995 of 28 December, establishing the rules applicable to the treatment of urban wastewater.
2. Royal Decree 509/1996 of 15 March, implementing Royal Decree-Law 11/1995, in its current version. The consolidated text incorporates amendments published up to September 2015.
3. Directive (EU) 2024/3019 concerning urban wastewater treatment entered into force in 2025 and must be transposed into national law by 31 July 2027. Therefore, as of August 2026, it constitutes a current European framework undergoing transposition, but should not yet be presented as replacing the current Spanish legislation.

Groundwater

1. Royal Decree 1514/2009 of 2 October, regulating the protection of groundwater against pollution and deterioration.

It should be applied together with the general framework for the protection of the public water domain and, where applicable, with the conditions established in the discharge authorisation.

Marine environment

1. Law 41/2010 of 29 December on the Protection of the Marine Environment, in its current version. It establishes the national framework for marine environmental protection and the prevention and reduction of marine pollution.

Discharges into the sea are also subject to coastal legislation and to the specific legislation of the autonomous community and the competent authority, depending on the type of discharge and receiving environment.

Water reuse

Where information concerns water reuse, the current legislation is:

1. Royal Decree 1085/2024 of 22 October, approving the Regulation on Water Reuse and amending various Royal Decrees governing water management.

References

Official sources

MITECO – Wastewater discharges

Information on discharge authorisation, monitoring and management. The Ministry for Ecological Transition highlights discharge authorisation as one of the main tools for managing water pollution and the need to address pollution sources at their origin.

MITECO – Wastewater discharges

MITECO – Manual for the Management of Discharges

Technical reference for managing discharge authorisations and their conditions.

Manual for the Management of Discharges – MITECO

INSST – NTP 473. Wastewater Treatment Plants: Biological Risk

Specific reference on biological risks associated with wastewater collection and treatment. INSST notes that these activities may result in exposure to both biological and chemical agents.

NTP 473 – INSST

INSST – BASEQUIM 024

Cleaning and maintenance in confined spaces at wastewater treatment plants: exposure to hydrogen sulphide.

Particularly useful reference for preventing occupational risks during maintenance and cleaning work.

BASEQUIM 024 – INSST

ISTAS publications

1. Guide to Discharge Control and Management. ISTAS, 2005.
2. Company Environmental Obligations. Guide for Workers' Intervention. ISTAS, 2010.
3. Guide to the Substitution of Hazardous Substances in the Company. Practical Manual for Intervention. ISTAS.
4. Prevention of Chemical Risks in the Workplace. Guide for Intervention. ISTAS.

These ISTAS publications are included as tools for workers' action and intervention, rather than as sources of current legislation. Their practical value is therefore maintained, while any outdated legislative references contained in them should be checked against the legislation currently in force.

Last update

August 2026