You probably do not need the filter but I think it is a good idea, solely because it should remove sand, silt and other sediments that may be present. If you use a filter with an activated carbon element, it should also be able to remove organic compounds that could effect the taste and odor of your water. Since you did not mention any problems with the taste or odor of your water, this is probably also not required but will not hurt. Filters, other than reverse osmosis, will not alter the mineral composition of your water. While some brewers, attempt to modify the mineral composition (profile) to more closely match the mineral composition where the particular style that they are brewing originated, this adds a whole level of complication and is not necessary to brew good beer and in your case is most likely not needed.