March 2008 Update

Our pottery water filters - how they're made and how they work

The pottery filter of this site is monolithic, in the sense that it is a single unit piece, consisting of a pressed and fired filter. Whether a candle or a disk, this filter is treated with a very tiny amount of silver.

The filter composition consists of 50% clay and 50% ‘grog.’ Grog consists of a clay that has been pre-fired, then milled to a granulate powder. The 50/ 50 mix is combined with a small amount of water, then formed by applying several thousand pounds of the force of a jack, into the die of a candle or a disk.

The pottery candle filter, shown below, is the basic monolithic filter element of

This is shown in the up-side-down position, prior to installation in the upper bucket.

A key in the forming of the filters is the application of the correct amount of force applied by a hydraulic jack, such that the subsequent filter will give the desired rate of flow. For the candle of our projects in Nepal and in Kenya the target flow rate has been 2.0 liters per hour, such that the water should be adequate for the needs of a family. The volume of the filter element has tended to be equal to the volume of filtered water, output per 20 minutes. In this way the E coli and other pathogens have 20 minutes of ‘residence time’ within the filter medium, wherein they are in sustained contact with the silver.

Shown below is the press, which is used for applying the force needed in pressing pottery filters. Note the car springs at the base, which allow the force of the jack to be applied both from top and from bottom.

Shown below is the gauge used in applying force. Equal force in every pressing helps ensure that the filters flow rate will be the same from one filter to the next.

Shown below is a candle, without the end caps. This was pressed to 6,000 pounds and will give 2.0 liters of filtered water per hour.

N.B. The filter technology here shown is 'open technology,' in the sense that any and all are free to pursue it.