A vacuum system for the brake booster of a motor vehicle includes a demand-driven vacuum pump and a vacuum line connected on one end to the vacuum chamber of the brake booster and connected on another end to an intake port of the demand-driven vacuum pump. The vacuum system may include a discharge device arranged on an exhaust air opening of the vacuum system for ensuring bidirectional air volume flow between the external surroundings of the discharge device and the exhaust air opening of the vacuum system, which preventing liquids from reaching the exhaust air opening of the vacuum system as an air volume flows from the exterior surroundings into the exhaust air opening of the vacuum system. The vacuum system may also include a check valve arranged between the intake port of the demand-driven vacuum pump and the connection to a vacuum chamber of the brake booster.