How does a gravity filter work (without a tap connection)?

Gravity does the work

A gravity filter (also known as a worktop filter) is two chambers stacked on top of each other. You pour tap water into the upper chamber, which holds the filters, gravity pushes it through the filter elements, and at the bottom you draw off the filtered water through the tap. No connection to the water mains, no electricity, no plumber: put it down and pour.

The element is the filter

Everything the system does happens in the elements: compressed carbon or ceramic that the water seeps through. How much an element holds back differs per brand and per substance; serious manufacturers supply test reports with reduction percentages per substance. More filter elements in the same housing mainly means: faster filtering, not better filtering.

Priming: the step everyone forgets

New black carbon elements (from Berkey and BOROUX, for example) first have to be 'primed': flushed under light pressure until the pores are full of water instead of air. If you skip that, the system runs painfully slowly or not at all and you think the filter is broken. Tools, instructions and a manual are of course included; allow a maximum of five minutes per element. Handy optional accessories can also be ordered with it, and we really recommend them: BOROUX Automatic Filter Primer Pump (electric). With white ceramic elements (such as Coldstream FTO PLUS) priming is not necessary; it does that itself (by soaking itself full). Do bear in mind that at first it can take up to 24 hours before any water runs through.

What you can expect

Count on a throughput of a few litres per hour per filter set: as an example, you fill the upper chamber and an hour later there is filtered water. That is why a household usually has enough with a water filter of 6 to 12 litres: the system works while you do something else. With black carbon elements (from Berkey and BOROUX, for example) the following applies: the better the priming has worked, the better they flow. This can therefore differ per filter and is entirely normal. With white ceramic elements (such as Coldstream FTO PLUS) the speed is constant and somewhat slower than with black carbon filters.