Exc: Ministers have been secretly warned that some English reservoirs are at risk of running dry, hitting water supplies to homes in the run-up to Christmas. The government’s emergency committee, known as Cobra, is meeting up to twice a week to discuss the situation in the southwest of England and Sussex. A secret “reasonable worst-case scenario” was drawn up, anticipating that several reservoirs’ water stocks could fall to 0 per cent — dubbed “day zero” — within weeks. Officials warned that without action, supplies to some homes could be affected, along with disruption to the construction of a nuclear power station and operations at a prison. Steps have been taken by ministers and water companies to try to mitigate the risks, which insiders stressed were already starting to push back the “day zero” dates. Experts on the government’s Scientific Advisory Group for Emergencies (Sage) have also been brought in to help review water companies’ modelling for protecting stocks for the weeks ahead. Heatwaves over the summer left half of England in drought. Sussex and the southwest were the most severely affected. Wimbleball reservoir, which supplies more than 400,000 people in Somerset, has 13 per cent of its capacity, while Ardingly, which serves 280,000 customers across West Sussex, is at 17 per cent, figures from yesterday show. Reasonable worst-case scenario plans were drawn up by the government, setting out a “day zero” envisaging Wimbleball and Ardingly reservoirs’ stocks being completely depleted by December. Subsequently, the government privately said it was told by South West Water that it did not anticipate Wimbleball running dry due to measures it had put in place. South East Water is also taking action that has shifted Whitehall “day zero” forecasts at Ardingly into next year. Even if the reservoirs did run completely dry, water companies would probably be able to transfer supplies from elsewhere. However, significant concerns remain in government about water disruption to properties supplied by Devon’s Venford reservoir in early November. “Day zero” risk monitoring has also started for Cornwall’s Stithians and Drift reservoirs. Water companies were asked to model the impact of water-saving measures, which have been scrutinised by members of Sage. Ministers were told that shortages could affect daily operations at HMP Exeter and the construction of Hinkley Point C, a nuclear power station being built in Somerset. Normal levels of rainfall over autumn and winter will not be enough to counteract the effects of the drought, which was extended to cover Yorkshire this month. Officials have calculated there will need to be 120 per cent of long-term average rainfall over the next six months for a nationwide recovery.