Signature reliability plays a fundamental and vital role in assessing the reliability measures for binary and complex systems. This study focuses on calculating the signature reliability of the physical processing unit (PPU) within a sewage treatment plant, utilizing universal generating function (UGF) techniques. A reliability block diagram is proposed to facilitate this calculation. UGF technique is applied to access the reliability measures like mean time to failure (MTTF), expected time and cost of the system, reliability function, signature, and tail signature of the system. Additionally, the Barlow-Proschan (B-P) index is computed to assess the sensitivity of the system relative to its subsystems, employing Owen’s formula. The results show that the expected cost of the system is determined to be 8.37747, while the B-P index highlights that subsystems A and B are the most sensitive subsystems among all.