Temperate glaciers respond sensitively to climate warming, yet in situ observations of their thermal and hydrological regimes remain sparse and often discontinuous. This study integrates four years of field measurements with numerical modeling to investigate the water and heat dynamics of Baishui River Glacier No. 1, a temperate glacier on Yulong Snow Mountain. Ice surface temperatures ranged from −14.43 °C to −0.07 °C (mean −6.11 °C), exhibiting strong seasonal variability. The seasonal active layer extends to approximately 15 m depth, below which ice temperatures stabilize near the pressure‑melting point (annual mean −0.13 °C) with an amplitude of only 0.11 °C (∼2.5 % of the surface amplitude). Simulated cumulative ablation (1.86 ± 0.07 m w.e.) closely matches observed values (1.83 ± 0.05 m w.e.; error < 7 %). A key finding is that conventional heat‑conduction models fail to reproduce temperatures in the upper 5 m, where liquid water from melt and precipitation dominates heat transfer. Below 5 m, conduction prevails and simulated profiles agree well with measurements. The presence of liquid water also decouples surface ice temperature from air temperature and introduces a nonlinear ablation–temperature response during the melt season. Our results indicate that water plays a fundamental role in the thermal dynamics of temperate glaciers, and meltwater-related processes must be explicitly accounted for in any investigation of past and future glacier thermal evolution.