GravityWorks 4.0L Filtr SystemThe reviews keep coming and one thing is clear, the GravityWorks system is changing how people filter water. Delivering four liters of filtered water is just 2. 5 minutes with no pumping, there's simply no easier or faster way to get safe water away from home. Ideal for bigger groups, the system's eight liter capacity eliminates both the worry and hassle of keeping plenty of water around for anything you need.