Ceramic filters

Firing creates a network of fine, winding pores in the ceramic. Water is pumped through the wall or seeps through by gravity. Particles and pathogens larger than the narrowest points of these pores stay mainly on the outer surface. Protozoa are reliably retained this way, bacteria depending on the pore size and quality of the filter.

Because the dirt collects on the surface, it can be scrubbed off. Each time, a very thin layer of ceramic is removed. That is why every element has a minimum wall thickness; some manufacturers include a gauge for checking when the element must be replaced.

Some elements are treated with silver to inhibit the growth of germs inside the filter itself; others contain a core of activated carbon for better taste. Neither changes the fact that viruses, salt and many chemicals can pass through the filter.

Before each use, check the ceramic element and the seals: cracks, chips or a crooked fit rule it out. Let cloudy water settle first or pour it through a cloth – this protects the ceramic, because you need to scrub it less often.

With a pump filter, the intake hose always stays on the raw-water side and the outlet points into a clean container. With a gravity filter, the raw-water vessel is on top and the clean-water vessel below; they must never be swapped. When the flow slows down, scrub the surface according to the instructions.

Cleaning requires care: hands, outlet and clean side must not come into contact with raw water. It is best to clean with clean water and wash your hands afterwards before reassembling the filter.

A cracked or chipped element lets pathogens through, and you cannot tell from the water. Check after any fall and before each use; replace if in doubt. Although ceramic is less frost-sensitive than hollow fibres, frost or knocks can cause fine hairline cracks. A filter whose integrity you cannot check counts as ineffective.

Ceramic filters do not reliably retain viruses. Where people live, where sewage or flood water is involved, or whenever you are unsure, additionally disinfect the filtrate – with chlorine, chlorine dioxide or by boiling. Whenever the authorities issue advice, such as boil-water notices, always follow it.

The filter does not help against salt and chemicals. Seawater or water suspected of containing fuel, pesticides or heavy metals does not become drinkable this way.

Pump filters with a ceramic candle are compact hand pumps for trips. They are robust against clogging because they can be cleaned, but they are heavier and slower than hollow-fibre filters. That makes them less suited to quick, lightweight supply on the move.

At home and in development work, pot and candle filters are common: a ceramic pot or filter candle sits between two vessels, and the water drips through by gravity. This filters larger volumes without effort – ideal for households, base camps and groups with time.

In each of these situations the multi-barrier principle applies: pre-clarify, filter and, where viruses are a risk, disinfect. Keep the filtered water in clean, closed containers so that it is not contaminated again.

Ceramic filters are among the oldest industrially made water filters and are used worldwide in household water treatment. Their performance depends heavily on manufacture and quality control. Retention claims apply only to the specific tested product – not to „ceramic“ in general, and certainly not to home-fired clay.

Compared with a hollow-fibre filter, ceramic is heavier, slower and more fragile, but cleanable, long-lasting and less frost-sensitive. Which filter suits you better depends on whether weight and speed or durability and volume matter more.

The flow is a good indicator of condition: when it slows, dirt is building up and it is time to clean. The wall thickness tells you how long the element will last – plan a replacement in good time.