Conventional water treatment processes (e.g., coagulation, flocculation, sedimentation, and filtration) are widely used for producing drinking water from surface water sources. Transient, gradual, or abrupt changes in source water quality that could compromise treatment effectiveness can be triggered by climate and related meteorological events, accidental or intentional contamination, security breaches, or other disruptions. However, the design principles that underpin the majority of existing conventional treatment systems predate climate adaptation considerations. This paper considers the adaptation capacity of conventional water treatment systems. A modeling framework is used to illustrate climate adaptation mechanisms that could enable conventional treatment systems to accommodate water quality impairments. Treatment system resiliency is explored in response to generic climate-relevant water quality perturbations such as extreme temperature variations and changes in the quantity and characteristics of solids, particles, and organic constituents. Promising adaptation options include modifying chemical parameters (e.g., types of chemicals, dosages, sequence of chemical addition, mixing intensity and duration), filter operations, and microbiological augmentation of existing physical/chemical treatment systems. The capacity reserve concept provides an organizing principle that could be useful for prioritizing climate adaptation strategies such as major or minor treatment/infrastructure modifications, system-wide upgrades such as off-line storage, operational changes in distribution systems, or the use of supplemental water sources including reclaimed or recycled water.