Nantes Social Water Pricing

This information was sourced from the European Commission, Joint Research Centre (2026): PSTW: Public Sector Tech Watch latest dataset of selected cases. [Dataset] doi: 10.2905/JRC.J1MWC9R PID: http://data.europa.eu/89h/e8e7bddd-8510-4936-9fa6-7e1b399cbd92. Licensed under Creative Commons Attribution 4.0 (CC BY 4.0).

Access to affordable water is a fundamental right, yet low-income households often struggle with utility costs. Traditional means-tested assistance programmes require complex application processes and frequently miss eligible beneficiaries who are unaware of available support. Nantes Métropole developed an open-source algorithm to determine eligibility for its social water tariff (Tarification Solidaire de l'Eau), guaranteeing that no household spends more than 3% of income on water for reasonable consumption of 30 cubic metres per person annually.

The algorithm calculates eligibility based on household income and family composition using data from the Caisse d'Allocations Familiales (CAF). For CAF beneficiaries with family quotient below the threshold, assistance is granted automatically. Other residents can apply at their town hall, where agents enter information into Deltas software developed in-house by Nantes Métropole. The algorithm processes data in real time, providing immediate eligibility determination.

The source code is published under the CeCILL-B open-source licence. In 2024, 5,866 households benefited from the social water tariff, receiving €407,153 in total assistance. Since January 2025, reformed Agence de l'Eau charges have been integrated into the pricing structure. The open-source approach supports transparency in public decision-making and enables other municipalities to adapt the algorithm for their own social pricing programmes.

Budget: Not disclosed