Gravity water filters are freestanding units. They are an excellent method of water treatment in areas with limited or no electricity as they don’t require electricity to run or a connection to a water supply. As such, gravity filter systems are used by many emergency relief organizations. The process is straightforward: pour water into the upper container. Gravity will then act on the water, pulling it down through two or more filter cartridges and then finally into the lower container. The lower container has a small tap built-in, allowing you to access safe, filtered water.