Photographers use a wide range of filters in their day-to-day work, but they're almost never mentioned in the realm of street photography. Seen as a raw, pure genre, it's assumed that street shooters rarely use filters. Should they?
For the vast majority of street photography work, a protective or UV filter is all you need. They preserve contrast and detail well. The UV filter serves no creative purpose, and that's its greatest asset. It's also a fantastic protective tool for your front lens element. Often, I've shattered my UV filters through knocks and bumps - and found my lenses perfectly intact. A replacement is often just a few dollars, compared to the hundreds that you might spend to repair damaged lenses. However, for all the advantages of the protective filter, the fact remains that they're creatively bland.
'a protective or UV filter is all you need'
If you're looking for a more creative image, you may want to consider the polarizing filter. Offering deep blue skies as a background for your street shots and cutting reflections in windows, it adds an interesting flair to your photos. Its effect also can't be replicated in most post-processing software, making it a popular choice of filter. There's certainly no shortage of options, although the circular polarizer is often the best choice for those who want to make fine tonal adjustments, a must for street photography. However, the effect of the polarizer is most striking in certain lighting conditions (facing 90 degrees away from the sun), so its effects aren't often applicable to the kind of on-the-go shooting that the street photographer favors.
On the more extreme side of the filtration spectrum is the ND filter. Stretching exposure times by as many as 20 f-stops, the dark elements of the filter can add a creative, streaky effect to your images. Try venturing out at night and capturing a minutes-long exposure of light trails for an unconventional perspective, or use a milder effect for panning and action. The results can be stunning, but their creative nature limits their use. Use the ND only in small amounts, or your images can quickly be overwhelmed by long exposures.
Though filters can offer a creative perspective on the street, the majority of your work should adhere to convention, or you risk losing the unique nature of the effects that filters bring. Use them in small amounts, and the results will truly stand out.