Water mains, or pipelines, are crucial for ensuring public safety, supporting economic vitality, and promoting human well-being. However, much of this infrastructure in the US dates back to World War II era (1940s), often necessitating repairs or replacements. Over time, a variety of analytical methods have been developed to optimize water main replacements. In addition to referencing highly influential academic journal articles, this chapter focuses on how US water utilities apply these techniques to decide whether to repair or replace aging infrastructure. This chapter traces the historical development of decision-making strategies in this field, noting significant paradigm shifts over several decades. With rapid advancements in Artificial Intelligence (AI) and ML (ML), new proactive approaches have emerged and are introduced to support water main replacement decisions. The chapter offers insights into the future of this field, highlighting its potential for ongoing innovation and the sustainable, resilient management practices of our water infrastructure.