Mechanical Pre-Filtration
The best way to keep rainwater clean is to prevent dirt and debris from entering the storage tank in the first place. Most systems accomplish this with a pre-filter, or in-tank filter. These filters typically have a stainless steel element and a plastic body.although some cheaper filters are all plastic. The element is often a stainless steel mesh or grid. Mesh fineness is expressed in microns - the smaller the micron, the higher the rating and the finer the degree of filtration. For example, the Wisy@ Vortex filter has a mesh rating of 280 microns (0.28 mm) and removes all but the finest particles without clogging the mesh.
Microfiltration
The particle filter can easily achieve a finer degree of filtration. Today these filters are generally sealed housings with a filter element or bag, made to trap very fine particles to deliver better water quality. Most filter elements or bags should be replaced on a regular basis when they start to clog. Some of the heavier filters are washable and reusable. The problem is that such filters need pressure to work well. They work by forcing the water through. Such filters are therefore generally used only on pumped water supplies.
More advanced models have a stainless steel element with back wash function for easy cleaning which can be done manually or automatically with a timer control.These are very effective, and reduce maintenance, but they are also expensive, and are usually only used in larger systems. Membrane technology is another advanced technique. Here water is pumped at very high pressure through a layer of material with microscopic pores that trap the particles. Again, this kind of equipment is normally only used on larger commercial projects.
Sanitization
Mechanical filters will remove particles from the water, but will not remove bacteria.lt doesn't matter if the water is only used for flushing toilets, washing machines and watering the garden. However, if rainwater is used for personal purposes as well,drinking, showering etc, or if there is a risk that water vapours can be inhaled (such as in garden centres or nurseries with sprinklers) then disinfection is a necessaryaddition.
This can be achieved in a number of ways such as chemical dosing, reverse osmosis (RO) or ultraviolet light (UV). RO systems are usually expensive and waste a lot of water, and dosing systems rely on hazardous chemicals (e.g. chlorine). Therefore, the most common method is UV disinfection which is safe and reliable if properly maintained.
The principle of UV disinfection is to use a certain wavelength and intensity of UV light for water flowing in a glass tube. This instantaneously kills all the microorganisms present in the water and thus disinfects the water. Changing the UV lamps is a simple,non-technical task, as it is done once a year.
Carbon Filtration
If rainwater is to be used for drinking (which is rare, but can happen if no other water is available) carbon filtration is recommended as an additional treatment. The passage of water through the carbon greatly improves the taste and odour and also changes the colour. This is the same technology used in standard household water filter pitchers and under sink units. Carbon also excels in removing chlorine and other volatile organic compounds or VOCs.
Modules of granular activated carbon can be incorporated into any rainwater system or can be used as a stand alone unit.
