One of the principal risks to public health is the lack of access to safe drinking water. The Millennium Development Goals by the World Health Organisation (WHO) focus on the target of halving the proportion of people without access to safe drinking water. The Sustainable Development Goal 6 ensures access to safe drinking water and sanitation to all.

As high as 2.3 million annual deaths among children occur due to diarrhoeal diseases in India that can be attributed to unsafe drinking water and poor sanitation and hygiene practices. The ideal solution to prevent waterborne diseases needs to focus on building access to safe and pathogen free drinking water at the point of use.

Household water treatment and safe storage (HWTS) is an effective and affordable means of providing safe drinking water at home. HWTS practices such as sedimentation, filtration, and disinfection are solutions that are easy and sustainable for making water safe for drinking.

A number of studies  have shown that HWTS practices have yielded considerable reduction in diarrhoeal diseases. Ceramic pot filter (CPF) is one of such point-of-use water filter.

What is a ceramic pot filter (CPF) and how it is manufactured?

CPF is used for household water treatment in many parts of the world. These filters are both locally and industrially produced. It is a low-cost water treatment technology that is capable of removing  microbial contamination and turbidity, and improves water quality at the household level.

CPFs are manufactured by mixing clay with combustible material. Currently they are fashioned in two variations - flat  and round bottoms. To make the ceramic filter, the clay and combustible material are mixed together with water until they form a homogenous mixture. The mixture is pressed into shape using a mould looking like a pot. This moulded pot is then dried in a shade for three to four days, and then in the sun.

The dried pots are then fired in a kiln. In the firing process, the combustible material burns out, leaving a network of interconnected micro pores. Water can flow through these micro pores. After the filters are fired and cooled, several quality tests, like a flow rate test, are performed. A flow rate test is the most verified test to ensure that the flow rate remains  between one to three L/hr. This is required to ensure that enough water is provided to the family and adequate contact time is maintained with the filter.

The moment flow rate test is performed and passed, the filters are air dried and impregnated with colloidal silver before distributing to customers. Silver is known  to have antimicrobial properties, and  has been used to kill bacteria, fungi and viruses. Silver as an additive is used to enhance microbial disinfection. Research shows that bacterial efficacy of CPF is increased with silver impregnation.

Operation

The raw water is poured into the ceramic pot filter. The water slowly passes down through the fine pores and is collected in the receptacle. The treated water is stored in the container until needed and is protected from recontamination. The tap at the receptacle is usually preferred for fetching treated water.

The CPFs are capable to remove iron, microbial contamination, and turbidity. CPF also reduces TDS to some extent.

The filter should be regularly cleaned with a soft scrub to remove any accumulated material. During the scrubbing, filter element retains the flow rate by removing the deposited particles from the pores. Any visible cracks or leaks must be checked over time to ensure its  effectiveness.

Contamination removal (treatment)

The pathogens and suspended particles are removed through physical processes like mechanical trapping, adsorption. Combustible material used in the mixture is used to ensure that pore size is small enough to prevent contaminants from passing directly into the filter. Colloidal silver acts as an antimicrobial shield, breaking the cell wall of the microbe and ultimately causing death.

<sup>1. Lantagne (2001)
2. Smith (2004)
3. Brown and Sobsey (2006)
4.  Vinka (2007)
5,  Low (2002)
6.  Van Halem (2006)
7.  Some additives to the clay may increase virus removal
8.  Not researched, however helminths and protazoa are too large to pass between the 0.6-3 μm pores. Therefore, up to 100% removal efficiency can be assumed.</sup>

Operating criteria

When the pot filter is full, flow rate is highest. Regular use of filter can lead to  accumulation of contaminants within the filter pores that  might reduce the flow rate. The flow rate, volume and supply are provided in the table below.

Robustness

• Receptacle container is used as a safe storage container.
• There are no moving or mechanical parts to break.
• Small cracks can occur due to impact or mishandling, which are not visible to the naked eye, but which may allow pathogens to pass through the filter.
• Poor transportation of filters can lead to cracking and/or breakage.
• Plastic taps in the receptacle container can break, metal taps last longer but increase cost.
• Requires supply chain and market availability for replacement filters and taps.
• Requires construction quality control process to ensure effectiveness.
• Recontamination is possible during cleaning; care should be taken to use clean water, not to touch the ceramic with dirty hands, and not to place the filter on a dirty surface.

Estimated Lifespan

• Up to 5 years, generally 1–2 years.
• Filter needs to be replaced if there are visible cracks

Maintenance

• Filters are cleaned by lightly scrubbing the surface when the flow rate is reduced.
• Soap and chlorine should not be used to clean the filter.
• Receptacle container, tap and lid should be cleaned on a regular basis.

Cost

The estimate cost of CPFs is about 450 to 750 INR depending upon the material and quality of receptacle vessel.

Production System

Please view this short video prepared by SM Sehgal Foundation to understand the production system of CPF. SM Sehgal Foundation offers training and technical support on this. The CPF produced by Sehgal Foundation is named as MatiKalp.

This article is a part of a series of articles on drinking water quality in collaboration with S. M. Sehgal Foundation, India and CAWST, Canada.

S M Sehgal Foundation addresses the most critical needs for water security, food security and community partnership and operates across ten states, in over 1,000 villages so far, reaching more than 2.5 million people. Through the water management program, the foundation encourages communities to harvest and store rainwater for direct use and/or replenish groundwater and surface water by building and restoring infrastructure in villages. Promoting safe drinking water through low cost household water treatment and storage in an important initiative towards SDG 6.

CAWST is a Canadian charity and licensed engineering firm. CAWST addresses the global need for safe drinking water and sanitation by building local knowledge and skills on household solutions people can implement themselves.

To learn more, please contact: smsf@smsfoundation.org OR lalit.sharma@smsfoundation.org