Antarctica's contribution to global sea-level rise (SLR) is deeply uncertain, with subglacial water suspected to play a critical role, yet its impact remains unclear. We demonstrate that water at the base of ice sheets influences sliding behavior and that its exclusion from models can underestimate SLR projections and delay the predicted onset of tipping points. Here we use the Antarctic Ice Sheet model (Elmer/Ice) to explore how different pressure determination methods at the ice base, with subglacial water present, affect SLR projections from 2015 to 2300. Our results indicate that incorporating subglacial water can amplify ice discharge across the Antarctic Ice Sheet by up to threefold above the standard approach, potentially contributing an additional $~$2.2 metres to SLR by 2300. Basin-specific responses vary significantly, with some scenarios advancing tipping points by up to 40 years. These findings underscore the critical need for integrating evolving subglacial hydrology into ice sheet models.