Italy's national framework for water resource management is established primarily by D.Lgs 152/2006 — the Environmental Code — which defines categories of water reuse and sets minimum quality standards for non-potable applications. For private homeowners, this decree is the starting point, but it does not replace regional and municipal rules, which vary considerably across the country.
The National Legal Framework
D.Lgs 152/2006 classifies rainwater harvested from roof surfaces as a secondary water resource. Article 99 permits its use for non-potable purposes — garden irrigation, toilet flushing, outdoor cleaning — provided the installation does not connect to the drinking water supply network.
The 2003 ministerial decree on reclaimed water (D.M. 185/2003), now superseded in part by D.M. 185/2020 for treated municipal wastewater, still serves as a reference point for quality parameters in residential greywater and rainwater reuse schemes where local authorities have not issued more specific guidance.
Permitted Uses at the Residential Level
For a single-family house, harvested rainwater may generally be used for the following purposes without additional authorisation beyond the standard building permit:
- Garden and vegetable patch irrigation
- Toilet and urinal flushing (with a dedicated distribution circuit)
- Washing machines in some regional frameworks
- Outdoor surface cleaning
- Filling swimming pools and ornamental ponds
Potable uses — drinking, cooking, showering — require treatment to potable standard and connection procedures that are practically prohibitive for typical residential installations. In practice, no residential system in Italy is approved for drinking use from roof catchment.
Regional Variation: Three Examples
Regulations diverge significantly at the regional level. The following three cases illustrate the range:
| Region | Key provision | Reference instrument |
|---|---|---|
| Lombardia | New construction with roof area above 100 m² must include rainwater cistern for garden and WC reuse | Regional regulation Piano di Tutela delle Acque |
| Toscana | Incentive-based approach; cisterns over 5 m³ qualify for reduced building permit fees | Regional water plan provisions |
| Puglia | Underground cisterns traditional in rural areas; specific exemptions apply for historic trulli structures | Municipal building regulations vary by comune |
Building Permits and Declarations
Installing an underground cistern generally requires a building permit (permesso di costruire) or at minimum a SCIA (Segnalazione Certificata di Inizio Attività), depending on the tank volume and whether excavation affects the structural envelope of the building. Above-ground tanks below a certain volume threshold — typically 2–3 m³ — often fall under the lighter comunicazione di inizio lavori (CIL) regime.
Homeowners in seismic zones (classified under NTC 2018) must also verify that buried structures comply with seismic ground conditions classified by the Istituto Nazionale di Geofisica e Vulcanologia (INGV).
Connection to the Sewage Network
The overflow outlet of any storage cistern must discharge to the surface runoff network, not the black water sewage network, unless local municipal regulations specifically permit mixed storm drain connections. This requirement is enforced by the local water authority (gestore del servizio idrico integrato), which varies by province.
What Changes in a Historic Centre
Properties within a centro storico face additional constraints. Exterior modifications — including pipes, gutters, and above-ground tanks — may require authorisation from the local heritage office (Soprintendenza per i Beni Architettonici). Underground installations are generally less restricted provided archaeological impact assessments are completed where required.
Practical Starting Point
Before commissioning a rainwater harvesting system, the standard process involves:
- Contacting the local Sportello Unico per l'Edilizia (SUE) at the municipality to identify which permit category applies
- Checking the regional Piano di Tutela delle Acque for water quality requirements
- Verifying that the intended installation area does not fall within a groundwater protection perimeter
- Confirming the hydraulic connection rules with the local water utility