Context:

If there is no safe drinking water within reach, water can also be treated at household level. In various ways: boiling it, chlorinating it, using SODIS, (bio)sand filtration, flocculants or ceramic candle filters. A relatively new option is the Ceramic filter with a Silver impregnated Pot-shaped filtering element (CSP model). Similar to high quality candle filters, the CSP model removes turbidity and 98-100% of all harmful bacteria that cause diarrhea and other waterborne diseases, like typhoid and cholera . It is now in use with 55.000 families in Central America and Cambodia where these filters are produced on a commercial base. Safe drinking water from the CSP filter will cost around US$ 3 per year per family.

 

A water filter (CSP model) used by a family in Nicaragua	How it works

How it works:

The ceramic filtering element of a CSP model is made porous by mixing clay with a material burning away during firing such as saw dust or rice husk. The element is impregnated with US$ 0.10 worth of colloidal silver which is a bacteriostatic ingredient that lodges on the pore walls of the ceramic material and acts like a magnet on the bacteria. The element is placed in a plastic receptacle with a faucet and covered with a lid. "Raw" water is poured into the filtering element, that contains 8 litres , then seeps through the pores thereby producing potable water at a rate of 2 to 3 litres per hour. With 3 fillings per day, more than 20 litres can be produced, or more if a "booster bottle" is used. Maintenance is easy (no gaskets or nuts) and eventual leakages are detected very soon. Cleaning is done by scrubbing the ceramic element when the pores get clogged. At the same time the receptacle should be cleaned to prevent bacterial growth. Although studies indicate that the silver in the ceramic element remains effective up to 7 years, it is recommendable to change the element every 2 to 3 years. Compared to the candle shaped models, the pot shaped model has more filtering surface and is easier produced with local skills. A disadvantage of this model is its vulnerability to breakage. Off-Factory Cost of a complete filter ranges from US$ 6 in Nepal to US$ 10 in Nicaragua; spare filtering elements cost US$ 3 - 4 in the market.    

Health and economic benefits:
A large-scale field study in Cambodia in 2003 (with 1,000 CSP filters) indicated that with the use of the CSP filter the cases of diarrhea reduced drastically, up to 50%. This resulted in 4 times less missed school days or work days. Using this filter also resulted in saving US$ 1- 2 per month on medicines and families that formerly used to boil water will now save US$ 1.4 per month on wood fuel. This means that a filter has a high "return on investment". In general in Cambodia a filter will "pay itself back" in less than 6 months. From then on, the filter will save 1 dollar/month or more. Thereby, it saved up to 22 working hours per month - for collecting firewood and for boiling - hours that can be used more productively.

A sustainable option:
The CSP filter is certified in several countries and used by organizations such as the Red Cross and UNICEF. Producing a CSP filter can be commercially attractive; profitable production and sales can lead to a sustainable distribution (after an initial support to production, quality control and promotion). To reach the lower-income families, cooperation is required between development organizations and local producers to promote and disseminate the CSP filter and to guarantee a proper use and maintenance as part of a broader hygiene education.

  Technical specifications:
 

More information:

The Ceramic water filter (CSP model)
Product sheet

In the absence of a potable water system, water at the household level can be treated with Point of Use (POU) methods such as Boiling, Chlorinating, SODIS, Sand filtration, or Ceramic candle  filters.  A relatively new option is the CSP model (Ceramic Silver impregnated Pot shaped filter). The CSP functions as a candle filter whereby the filtering element has the shape of a pot. Similar to the candle filter, the CSP removes turbidity and harmful bacteria that cause waterborne diseases such as diarrhoea. It is being used by around half a million people in Central America and Asia at a cost of US$3 per family per year.     

How it works
The ceramic filtering element of a CSP model is made of a mixture of selected clay and inflammable material, for instance rice husk. When firing the element in a kiln the husk burns leaving small pores which can retain turbidity and most of the bacteria when filled up with water. The element is impregnated with colloidal silver, a bactostactic  that acts like a magnet on bacteria that are not retained by the small pores.
Evaluations indicate that the CSP produces drinking water that complies with the WHO standards for turbidity and bacteria. It can remove 99.9 % of harmful bacteria that cause diarrhoea and other waterborne diseases. It does not remove arsenic, pesticides or other toxic material. For further information, see  www.potpaz.org.
The model can produce potable water at a rate of 2 to 3litres per hour. Maintenance consists of scrubbing the ceramic element when the pores are clogged, and cleaning the receptacle to prevent bacterial growth. While studies indicate that the silver in the element may work for up to 7 years,  it is recommended to change it every 2  years. 

Production of filters in Ghana	Different sizes of filters in Nicaragua

Application

The CSP, if well maintained, produces sufficient drinking water for an average household of 5 persons.  Compared to candle filters the pot-shaped model has a bigger capacity and is easier to produce locally; leakages are easier to detect so there is less risk in use. Field studies show that  a filter is “paid back” within 3 to 6 months owing to savings on expenses for medicines, fuel wood and labour.

New developments
Practica works with other organisations on improvement of the combination of ceramic and silver.  A new version is the so called “suction filter” that combines a double disk or ceramic candle with a hose. This concept will be smaller and even cheaper than the CSP model and reduces the risk of recontamination as there will be no storage vessel. Consult the Practica website for the latest developments.