Filters also remove bigger contaminants like leaves, silt, dirt, and sand. If the water is cloudy or has floating material in it, you should filter it even if you plan to boil or disinfect it. Filtration systems with absolute pore size less than or equal to 1 micron filter (NSF Standards 53 or 58 rated “cyst reduction / removal) have a high effectiveness in removing cryptosporidium and giardia.