Evaluation of soap as the cause of premature blockage in personal water filters

Rural families in the Dominican Republic have limited access to a continuous supply of potable water. Personal water filters, consisting of two 5-gallon buckets, a ceramic filtering element, and a spigot, are used for water purification. Field experience shows that approximately 20% of the ceramic elements prematurely become blocked and filter slowly or do not filter. Because of early obstruction of the filtering element and cultural tendency to clean regularly with soap, experiments were performed to determine if soap is the cause of this problem. Six personal filters were assembled and allowed to filter multiple trials of water from a local source. In three of the units, the ceramic filtering element was cleaned with soap prior to each trial, and in the other three filters the ceramic element was rinsed with water prior to each trial. After 12 hours the volume of water purified was measured. Following 19 consecutive trials, the ceramic elements cleaned with soap consistently filtered 10% more water than those not cleaned with soap. After scrubbing the non-soap filtering elements with a brush to remove sediment buildup, the six filters filtered at similar rates. These experiments indicate that soap does not have a negative effect on the filtration rate and that soap is not likely the cause of the premature blockage of the filtering element.