Dirt filters and side stream filters prevent particles suspended in the water from blocking or damaging equipment and systems. Dirt filters are usually placed in the supply water of a softener of reverse osmosis unit. Side stream filters are usually used in heating systems.

Iron and manganese can damage equipment and systems and are therefore often reduced to a minimum by treating the water. To remove iron and manganese from water, the source water is given intensive exposure to oxygen. After a series of subprocesses, passing through oxidation, hydrolysis, flocculation and precipitation, iron and manganese are eventually filtered out. In this process the divalent soluble forms of iron and manganese present in the water are converted into extremely poorly soluble forms. The iron and manganese particles resulting from this physical chemical process (also known as electrokinetic adsorption) can then be filtered out using calcined/heat-treated and sieved river sand, selected according the source of the water supply and the desired end result. The first precipitate formed, iron hydroxide, has a positive effect on the remaining formation of precipitate for both iron and manganese. Due to this catalytic action, clean filter sand must be given sufficient time to act before the iron removal process runs efficiently. The same principle applies for the manganese removal process. The ultimate quality of the water after iron removal (deferrised water) is dependent on various parameters such as the pH value (acidity) of the water, the oxygen concentration, the buffering capacity of the water source, the flow rate and the choice of filter medium.