Ceramic Candle Filter

The use of ceramic material for the filtration of drinking water is one of the oldest drinking water treatments. Nowadays, the ceramic candle filters and the colloidal silver filter (see also the colloidal silver filter factsheet) are the most widely used. The devices consist of two compartments, which allow simultaneous treatment and save storage of the drinking water. Candle filters are used in various countries and produced by a range of manufacturers around the globe.

Ceramic candle filters basically consist of an upper and a lower container, one or more ceramic candles in between, a tap and a lid. Usually the containers have a diameter of about 30 by 25 cm depth for a treatment capacity of about 8 L and a flow rate of 1-2 L per hour per candle. The ceramic candles are screwed into the base of the upper container. To the lower container is attached a tap that allow to withdraw safe water without risking recontamination. A lid is placed on top of the upper container to prevent contamination.

Candles can have very slow flow rates, so it is common to use two or more candles in one filter. The candles are made up of clay and the container can be made from plastic, aluminium, copper, steel or clay material. Though clay containers keep water cold and tasty, due to its fragile nature other materials nowadays replace it.

Water is poured into the upper container and flows through the candle and collects in lower container. Turbidity, suspended materials and pathogens are removed from water through mechanical trapping and adsorption in micro-scale pores of ceramic candles. Colloidal silver is sometimes used in candle for more effective pathogen removal.

Water should be poured slowly into the container, not above the candle as regular water pressure may damage fragile candle. Candle needs to be replaced if any cracks are found: cracks will reduce the effectiveness since water can pass through that crack without being filtered through the ceramic pores.

Candle needs regular cleaning, particularly when the flow rate slows down. The candle is cleaned by (slightly) scrubbing the candle surface with a soft scrubber brush or cloth to remove any accumulated dirt. Only clean water (no soap, chlorine or other chemicals!!!) should be used for cleaning. The candle should not be touched with dirty hands, and not placed on a dirty surface during cleaning. Storage containers, tap and lid should be cleaned on a regular basis using soap and water.

Ceramic candle filters are effective in removing bacteria, protozoa, helminths and turbidity from water. It also removes some viruses and iron and taste, smell and colour of water are improved. The effectiveness of the filter also depends on the production quality, the initial water quality, and the handling practices of users. Highly turbid or iron containing water may plug candle pores easily so that container and candle need to be cleaned more frequently. In this case, the water should be pre-settled before pouring it into filter. It is recommended to use raw water with less iron (<0.3mg/L) and turbidity (<5NTU).

Summary of Ceramic Candle Filter Technical Performance.

* Not researched, however helminths and protozoa are too large to pass between the 0.6-3 μm pores. Therefore, up to 100% removal efficiency can be assumed. Source: MATTELET (2006); CLASEN & BOISSON (2006); FRANZ (2004); CHAUDHURI et al. (1994); HORMAN et al. (2004) in CAWST (2011)

Candle filters can be manufactured at a local level and contribute to the development of local commerce. Local production process provides financial supports to household and voluntary labours. However, the production of ceramic filters is a lengthy process and a quality control process is required to ensure candle filter‘s effectiveness. Quality can be affected by variations in clay composition across geographic regions. Variability in weather conditions also makes long-term production planning difficult, and lack of storage can complicate storage of filters. The fragility of ceramic filters can make their transport difficult. A supply chain and market availability for replacement of candles and taps is required. Filters typically come with illustrated instructions in market.