The UK government has proposed different low-carbon energy system options that lead to meeting its greenhouse gas emissions target of 80% reduction on 1990 levels by 2050. While these energy system options meet emission targets at feasible economic cost, water requirement for the deployment of the proposed energy technology mix is not adequately accounted for. This may become critical, as some of the proposed energy technologies are relatively more water-intensive, and could result in significant future water resource constraints. Previous studies have analyzed the potential water resource constraints of future energy systems in the UK at national scale. However, water must be considered as a local resource with significant regional variability. This paper uses a linear spatial-downscaling model to allocate water-intensive energy system infrastructure/technologies at catchment level, and estimates water requirements for the deployment of these technologies for the Committee on Climate Change Carbon Budgets in 2030. The paper concludes that while national-scale analysis shows minimal long-term water related impacts, catchment level appraisal of water resource requirements reveals significant constraints in some locations. This has important implications for regions where the water-energy nexus must be analyzed at appropriate spatial resolution to capture the full water resource impact of national energy policy.