The water footprint is an environmental sustainability indicator gaining increasing importance for certifications and labels in agricultural production. Processed tomatoes require considerable amounts of water, and existing studies on water footprint present methodological uncertainties, often failing to account for the impact of different calculation strategies for water requirements. Furthermore, the growing challenges of water scarcity demand smart and innovative irrigation solutions. The aim of this study was to explore the impact of the calculation method and water requirement return strategy on the water footprint of processed tomatoes. This study was conducted during the spring–summer periods of 2022, 2023, and 2024 in two different coastal areas of Sicily. The processed tomato variety tested was Tayson F1 (Nunhems®). Water requirements were estimated using the FAO's CROPWAT 8.0 model, calibrated and validated for field data, as well as moisture (TEROS 12) and matric potential (TEROS 21) sensors placed in the soil. Additionally, two different irrigation strategies were evaluated for each of the two-water requirement return methods: full restoration of crop water requirements (FULL: 100% CWR) and regulated deficit irrigation (RDI: 70% CWR from transplanting to first flower emission; 100% CWR from first flower emission to fruit enlargement; 70% CWR from fruit enlargement to harvest). The CWR values, obtained for each calculation method and irrigation strategy, were used to calculate the total water footprint according to the guidelines of the Water Footprint Assessment Manual. Specifically, the CROPWAT 8.0 model overestimated the CWR by approximately 50 mm compared to the moisture sensors, resulting in an increase in all components of the water footprint. The results suggest not only inconsistencies in the classification of tomato production systems based on water footprint but also recommend the development and broader implementation of smart systems for determining CWR. Furthermore, this study highlights the potential to mitigate water scarcity challenges. Adopting a smart integrated approach becomes imperative for accelerating water security in sustainable agriculture, ensuring resilient and efficient water supply for future agricultural demands.