Backwashing filters are used for the physical properties of water, which includes removing color, taste and odor. Backwashing filters are also used for chemical control: fluoride removal, chloramines removal. For instance you can have iron discoloration, which is a physical property of the water and you can also have odor issues such as hydrogen sulfite/rotten-egg odor and by using a select medium or combinations of media Dime Water, Inc. can take care of both in one tank.
Because we are dealing with harsh waters it is very important that we use tank and valve materials that are not going to be compromised by the water conditions. Quite often there is pre and post treatment to backwashing filters. The pretreatment will often be a chemical feed system, feeding something like chlorine or hydrogen peroxide, perhaps ozone will help with the oxidizing properties and will remove iron and manganese. It is not unusual to put a post cartridge filter after a media filter, let the media filter do the 99% of the work and then just any trace amounts of the contaminant would then be picked up by the post cartridge filter.