This study on the Performance of Legacy Proprietary Billing and Collection System in San Pablo City Water District was conducted using a descriptive method approach. This study hypothesized that there is no significant relationship between the level of performance of the Legacy Proprietary Billing and Collection System and the level of capability of SPCWD for In-House System Development in the San Pablo City Water District. Using the descriptive research design, twenty (20) personnel of SPCWD, of which ten (10) from the Billing and Accounts Division of the Commercial Services Department as the authorized users of Billing Module, five (5) from the Treasury and Budget Division of Financial Management Department as authorized users of Collection Module, and five (5) from Information and Communication Technology Section of Office of the General Manager as the in-house system developers served as the respondents of the study. After the validity test of the experts, a self-constructed questionnaire was used as the main instrument to gather adequate data and information in this study to ensure they adequately represented the construct and administered the instrument to the selected respondents. The 4-Point Likert Scale and its Verbal Interpretation for Level of Performance were utilized to determine the level of performance of the Legacy Proprietary Billing and Collection System of SPCWD in terms of user satisfaction, technical support, and scalability and the Level of Capability in terms of peopleware, hardware, software, and financial resources. Data were analyzed using descriptive and inferential statistical treatments such as weighted mean, standard deviation, and Pearson Product Movement Correlation Coefficient (r). Among the three indicators measuring the level of performance of the Legacy Proprietary Billing and Collection System of SPCWD regarding user satisfaction, technical support and scalability was interpreted as needs improvement. Four indicators measuring the Level of Capability of SPCWD for in-house System Development were found to be very capable. These were peopleware, software, hardware, and financial resources. Therefore, the hypothesis stating that there is no significant relationship between the level of performance of the Legacy Proprietary Billing and Collection System and the level of capability of SPCWD for In-House System Development in San Pablo City Water District was rejected. The following conclusions were drawn based on the findings: It suggests the necessity for refining user experience, enhancing technical support mechanisms, and ensuring scalability to accommodate future growth and demand. By addressing these areas, SPCWD can strive towards optimizing the performance of its billing and collection system, ultimately leading to higher levels of satisfaction and efficiency. Capability bodes well for SPCWDs ability to innovate, customize solutions, and address specific organizational needs through internal development efforts, fostering greater independence and flexibility in managing its technological infrastructure.; in-house system development allows SPCWD to create customized solutions tailored to its unique needs and operational requirements. This capability ensures that the software and hardware systems developed align closely with the organizations processes and workflows, potentially leading to improved efficiency and effectiveness.