Question: How does the process of cleaning water via metals actually work?

Harriet Aitken answered on 16 Jun 2014:

The process relies on the metal corroding, so we need to choose a metal that will rust easily over a range of water conditions. You need to think about a few keys things, like the pH (the acidity of the water – at low pH corrosion is usually fast), the amount of oxygen dissolved in the water (a lot of oxygen also usually means corrosion will be fast) and also what other chemicals might be present (other chemicals that might not actually be harmful, may stop the dangerous chemicals from being removed because they react faster).

Iron corrodes well over a wide range of conditions and is also fairly easy to get hold of as it is one of the most common metals on earth making it cheap. Corrosion is caused by an electrochemical reaction – chemicals are made up of neutrons, protons and electrons – electrons are unique because they can sometimes be given away by or accepted by chemicals easily by an electrochemical reaction like corrosion. During corrosion, iron looses electrons which then means it is free to go and react with another chemical, like water and/or oxygen, to form rust.

Rust is very reactive, and is able to attract certain chemicals that are harmful by a process called adsorption. Adsorption means that the chemicals are attracted to each other and so the chemical is then removed from the liquid into the solid rust. Rust can then easily be removed by using a filter – the most common filter that I use is actually sand as the small grains of sand are able to remove the rust and reacted chemicals giving you clean water.