Water storage tanks must remain operational post-earthquake to sustain emergency response and public health. Seismic-induced liquid–structure interaction generates hydrodynamic pressures that produce critical stresses on structural components, often leading to failures such as cracking or leakage in concrete tanks. Consequently, their functional importance and damage susceptibility demand rigorous design standards to ensure seismic resilience. Iran's principal design standard for concrete water storage tanks, Publication 123, was last substantially revised in 1993. However, post-earthquake observations and advances in global seismic design practices later revealed significant shortcomings in its provisions. To address these gaps, the standard underwent a comprehensive revision, integrating modern hydrodynamic models, load combinations, and performance-based criteria from ACI 350.3, thus markedly enhancing the seismic performance and reliability of such infrastructure. This paper presents a comprehensive comparative analysis of the 1993 and 2015 editions, examining the evolution of seismic design provisions for buried, non-buried, and semi-buried concrete tanks. The analysis reveals significant improvements in seismic zoning, importance factor differentiation, response modification factors, pressure distribution modeling, and load combinations. The practical implications of these changes on reinforcement detailing, wall thickness, and overall structural performance are discussed, and recommendations for future code development are provided.