John, just because water looks clear to the naked eye does not mean it does not contain tiny organic particles, protazoa or bacteria that are of course invisible to the human eye and are only visible under a microscope. The Sawyer mini will filter down to 0.1 microns, and anything that small is definitely invisible without a microscope. So if your Sawyer mini appears to be blocked, then you have either failed to back-flush it enough or the clear water you speak of is obviously not as clear and pure as it looks!