Many hydraulic structures along the Dutch waterways were designed and constructed prior to the implementation of structural reliability methodologies in structural design. Hence, it is crucial to accurately quantify their residual service life for better replacement and renovation planning. However, the current standards for the assessment of existing structures (i.e. NEN 8700), which use a semi-probabilistic approach, are insufficient. This is due to (1) their reliance on a fixed reference period, which is not suitable for assessing at what point in the future the structure will not meet the reliability requirements, and (2) their limited use of inspection and testing data, as well as evidence that the structure has survived for a number of years. To overcome these limitations, this research focuses on developing a generic methodology for a reliability-based end-of-life assessment using a full probabilistic approach. This methodology involves evaluating the structural reliability on an annual basis, thereby providing a more precise prediction of when a structure will no longer meet the safety requirements. It includes defining limit states for various failure mechanisms, developing methods to incorporate inspection and testing data as well as information about past performance. Initially, this methodology is applied to case studies of a siphon and a sluice that are approaching their design service life. By refining this methodology based on lessons learned from these case studies and then extending it to typologies of hydraulic structures, this research aims to enhance the accuracy of lifespan predictions and the prioritization of maintenance and renovation efforts for hydraulic structures, thereby making decision-making processes more efficient.