It is best to check the contents of the water reservoir at every fill-up. On average, the contents of this reservoir will last to approximately 14 to 16 gallons of fuel. It varies from vehicle to vehicle because each one is different and it is also dependent on the driver and driving conditions. During cold weather, any temperatures below 50 degrees, it is necessary that isopropyl alcohol, 70% by volume, be added to act as an anti-freeze. As an added boost for racing vehicles, a 50-50 mixture of water and methanol can be used or a 50-50 mixture of isopropyl alcohol (70% to 99% by volume) and water. You now have an engine that is part hydrogen engine, part formula engine, part gasoline engine and part steam engine. This makes for a very healthy engine. Mean and clean machine!