Smart meters generate detailed information about the energy consumption patterns of the consumer, increasing the risks of data breaches, identity theft, and other forms of cyberattacks. Many existing solutions still suffer from computational complexity, time consumption, and security vulnerabilities. To address these issues, this paper presents ReWaP, a Reversible Watermarking and Paillier encryption-based privacy-preserving scheme to ensure data confidentiality, integrity, and authenticity in smart meter systems. This unique approach protects user privacy and maintains the security of the meter reading. A comprehensive security analysis verifies the resilience of the proposed scheme against multiple known attacks. The implementation using a RIOT OS and Nucleo microcontroller board resulted in low computational overhead and minimal impact on communication bandwidth. The experimental results and performance analysis demonstrate that the proposed scheme effectively balances data privacy, system reliability, and operational efficiency, making it an effective solution for modern smart metering infrastructures.