Decree 18/2023: Everything You Need to Know About Water Disinfection

Decree 18/2023: New Regulation on Water Disinfection

Legislative Decree No. 18 of 23 February 2023, in force since 21 March 2023, transposes Directive (EU) 2020/2184 and thoroughly updates Italian legislation on the quality of water intended for human consumption.

The new regulatory framework is based on four pillars:

1. Protection of public health through a preventive approach
2. Universal access to safe and clean drinking water
3. Risk management across the entire water supply chain
4. Greater transparency and access to information for citizens

In this context, water disinfection inevitably represents one of the most critical topics, with direct operational implications for operators, administrators, and healthcare facilities that must ensure proper microbiological risk management.

Drinking Water and Microbiological Risk: What the Decree Provides

Given the potential health implications of microbiological risks associated with water, Legislative Decree 18/2023 identifies key parameters for determining potability—namely Enterococci and Escherichia coli, which must be absent.

One of the major innovations introduced by the decree is the inclusion of Legionella as a potability parameter, specifically for internal building networks: in other words, the presence of Legionella in concentrations exceeding 1000 CFU/L (this is the threshold set by the decree) renders the water non-potable and prohibits its use.

In addition to potability parameters, the decree establishes indicator parameters whose monitoring contributes to the microbiological quality and safety assessment of water. These include Clostridium perfringens, coliforms, and colony counts at 22°C.

Disinfection: Obligations and General Principles

Article 8 of Legislative Decree 18/2023 stipulates that, if disinfection is applied, it must:

• Be effective against pathogenic microorganisms;
• Ensure a sufficient and persistent residual disinfectant;

• • Not result in the significant formation of by-products hazardous to human health or the environment;

  • Be an integral part of a risk-based approach to assessment and management.

Moreover, all implemented measures must be documented and traceable for verification by the competent authorities.

When is Water Disinfection Mandatory?

The decree does not mandate universal disinfection of all drinking water, but acknowledges its importance as a fundamental control measure. Specifically, when disinfection is part of the water treatment or distribution process, its effectiveness must be verified and guaranteed. It is also required that:

• The concentration of disinfection by-products be kept as low as possible, without compromising treatment effectiveness;
• Chemical reagents used do not produce residues that would compromise compliance with quality standards;
• Compliance with parametric values and general obligations defined in Article 4 of the decree is ensured.

Furthermore, disinfection is considered appropriate and necessary, within the context of risk assessment and management, when:

• Documented or potential microbiological risks are present;

• The distribution systems are complex or extensively branched;

• The buildings are considered high-priority, such as hospitals, healthcare facilities, schools, or other sensitive environments;
• There are conditions favourable to the formation of stagnation zones or extended water residence times in the pipelines.

Criteria and Requirements for Disinfection Systems

The decree does not prescribe a specific solution but imposes compliance requirements based on:

• Demonstrated microbiological efficacy (supported by studies and technical documentation);

• Suitability of materials and substances used, in accordance with Ministerial Decree 25/2012 and the REACH Regulation;

Absence of release of hazardous secondary contaminants.

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Attention to Disinfection By-Products (DBPs)

Decree 18/2023 does not set limit concentrations for disinfectants, but indirectly regulates their use by imposing containment of disinfection by-products (DBPs), such as:

• Trihalomethanes (THMs)
• Haloacetic acids (HAAs)
• Chlorites and chlorates

These substances, recognised as hazardous to human health, must remain within the limits specified in Annex I, Part B of the decree, and their levels must be monitored through regular analytical testing.

Water Safety Plans and Microbiological Risk Management

The decree mandates that all operators adopt a Water Safety Plan (PSA o WSP), in accordance with the World Health Organization’s guidelines.

In this context, disinfection must therefore be framed within a holistic strategy, which includes:

• Preventive analysis of microbiological risks
• Identification of critical control points
• Definition of control measures (e.g. residual disinfectant thresholds)

Emergency plans to ensure rapid response capacity

Penalties for failure to disinfect and operators’ obligations

Failure to implement effective disinfection measures in the presence of risk may result in:

• Administrative sanctions amounting to tens of thousands of euros
• Mandatory reporting and immediate corrective actions
• In severe cases, criminal liability due to health risk

Healthcare facilities and public water operators must therefore implement certified, documented, and verifiable systems.

In Summary

Decree 18/2023 introduces a paradigm shift: water disinfection is no longer considered a secondary technical measure, but an obligation integrated into public health and environmental risk management.

Knowing, applying, and properly documenting water disinfection today represents an essential technical and regulatory responsibility.