How Siphon Filters Work

Siphon filters rely on the simple natural force of gravity to purify water.
The filter above is capable of making safe water from water contaminated with bacteria. It does this without the need of any external energy source or chemical additives.
The filter itself is a ceramic candle. It is attached to a simple adapter made of plastic tubing.

The filter is placed in the upper container, which is filled with contaminated water. The user sucks on the end of the tube until a flow is established, then quickly lowers the tube to a position lower than the container. From that point the siphoning action pulls water through the tube. The end of the tube is placed into a second container to catch the product water. The filter will continue to produce water until the upper container is empty.

More about siphon filters

Siphon filter make excellent emergency filters because they operate without an outside energy source and without water pressure. No elaborate equipment is needed.
They can also be used as camping or hiking filters, to purify water from a lake or stream, and even as everyday water filters. They work best with ceramic cartridges, which remove bacteria and cysts, or with certain carbon filters, which remove chemicals.
The simple filter shown above can treat up to 70 gallons a day if the water is warm, or less than half that if the water is cold. In terms of volume, it easily outperforms expensive canister-style pour-through filters.
Siphon filters are among the least expensive water filters to purchase and to operate.