CONTEXT: Water-saving irrigation technologies (WSITs) are widely promoted in arid and semi-arid agriculture to improve water-use efficiency, yet installation does not necessarily translate into stable operation. This study conceptualizes this installation-operation gap as an irrigation adoption paradox: water-saving irrigation systems are formally adopted or installed, while their practical use remains selective, intermittent, or reversible, especially among resource-constrained smallholders. OBJECTIVE: This study examines how smallholders regulate WSIT use after formal adoption and explains why technologies that appear successfully diffused may fail to become embedded in everyday irrigation practice. It focuses on how farmers adjust use intensity, deployment scope, timing, and reversal thresholds under interacting external pressures, household capacities, and enabling support conditions. METHODS: We conducted a Q-method study with 45 smallholders in the Guanzhong Plain of Shaanxi Province, China, complemented by follow-up semi-structured interviews. Participants ranked 40 statements covering market and financial feasibility, operational capacity and farm-technology fit, performance and reliability feedback, policy and institutional pressure, enabling support conditions and social learning, and ecological scarcity and risk orientation. Q-sorts were analyzed in PQMethod using centroid factor extraction and varimax rotation, and interpreted through factor arrays, distinguishing statements, consensus statements, and interview evidence. RESULTS AND CONCLUSIONS: Four adaptation logics were identified. Performance-driven stabilizers expand use after verifying yield and income stability; cost-risk accountants deploy WSITs selectively under affordability and payback uncertainty; policy-compliance adopters engage with WSITs through project incentives but remain vulnerable to installation-operation gaps; and risk-averse retreaters require high reliability before trusting the technology in critical irrigation periods. These logics differ in motivation and decision pathway, yet converge on a common practical threshold: WSITs become sustainable only when they are operable, repairable, manageable, and compatible with farm-level production routines. The findings show that unstable WSIT use is not simply a result of weak awareness or incomplete diffusion. Rather, it reflects rational post-adoption regulation under systemic traps, where the pressures that bring technologies into farms are not matched by the capacities and support conditions required to sustain everyday operation. SIGNIFICANCE: By theorizing the unresolved transition from technology entry to practical embeddedness, this study advances post-adoption research beyond the conventional focus on uptake, sustained use, or discontinuance. It shows that diffusion success can coexist with incomplete farm-level adaptation when the conditions that promote adoption are not matched by those that sustain everyday operation. The findings therefore shift the evaluation of agricultural innovation from whether technologies are delivered or adopted to whether they become operable, durable, and trusted components of farming systems.