Organic material inside gutters or cisterns will release tannins into the water supply, which can discolor the water (like tea leaves). While not harmful, it can look unpleasant and reduce UV sterilization effectiveness. This filter element will remove tannins. This filter element would install inside one of our 20" x 4.5" Filter Housings , and lasts about 2 years. Made in Hong Kong. NSF/ANSI 44 and 61 approved.