This represents much of the total mass of the vehicle, making the car heavy (an internal combustion-engined car requires no boiler), and requires careful attention from the driver, although even the cars of 1900 had considerable automation to manage this. The single largest restriction is the need to supply feedwater to the boiler. This must either be carried and frequently replenished, or the car must also be fitted with a condenser, a further weight and inconvenience.