The mid-20th century through the early 1980s saw water treatment research coalescing around membrane-based separation as a unifying framework for purification and desalination, enabling selective removal of salts and contaminants from large water streams. Concurrently, disinfection research foregrounded the chemistry of chlorine with natural organics, haloform formation, and the emergence of analytical monitoring for total organic halogen, driving improved safety assessments. Analytical chemistry and process analytics advanced methods to identify neutral contaminants, profile municipal water quality, and standardize examinations across water systems. Biological and microbial studies highlighted virus recovery dynamics and the influence of surface charge on membranes and algae, shaping purifier design and operation. Collectively, these threads fostered a systems-oriented view of water treatment where membranes, disinfection byproducts, and analytical quality-control co-evolved.