The Earth has been filtering water naturally through the Hydrologic cycle since rainfall began. The continuous cycle whereby water falls from the sky in the form of rainfall, through percolation where the water passes through the soil and substrate to join the groundwater. This groundwater joins underground streams and eventually feeds rivers. The sun causes evaporation to occur and the moisture returns to the
sky to condense and fall again. As the rainwater passes through the soil and rock on it’s way to the underground streams, the process of filtration has already begun. Many of the suspended solids, the impurities contained in the water are left behind.
Depending on the uses we have for the water, various techniques can be employed to improve the quality to the point whereby it is suitable for purpose. For example, for agricultural applications where the water is being used for irrigation, there may be no further filtration required. Whereas if the water is to be used for human consumption there will be various treatments required to ensure that the water is fit for use.
Filtration describes the process or processes of separating suspended matter from a liquid. In it’s simplest form it involves passing the liquid through a column of granular media. These granular materials
are selected for their differing abilities to trap particles based primarily on their size.
By utilising this principle a multi stage filter, beginning with a coarse media will trap large particles, if the next stage uses a finer media it will trap smaller particles and so on. Other materials are used to achieve other results. Mechanical screens of varying mesh sizes will offer different outcomes. In some cases porous materials such as paper are used, much in the way we would use to filter coffee, where they allow the full flavour through, but retain the coffee grounds. In some cases, depending on the size of the contaminants present it may be necessary to use paper, polypropylene or even a membrane material to remove undissolved suspended particulates. Where these contaminants discolour, cloud or otherwise effect the clarity of the water this is known as turbidity. A list of the “usual suspects” where turbidity is present would be fine silt, sand, organic matter such as tannins in boggy country. Also precipitated iron, bacteria or algae, which may be present in both surface and well water
Well designed tank type media filters are capable of removing these suspended solids down to about 10 micron and with specialist media are able to take this down to around 3 micron. Filters for the home and business: Filters used in these environments are based on the same principles as large industrial filter systems. The main difference being that
industrial filter systems often require ongoing maintenance and attention to ensure optimum performance. In small business and domestic applications, the robustness of the design so as to require minimal maintenance is a major consideration in selecting equipment and media. Where regular monitoring and maintenance are not a realistic expectation it is essential that system design reflects this.
Apart from cartridge changes on a six monthly or annual basis for drinking water kits most maintenance on water treatment equipment would be annual and should be carried out by trained personnel.