A gravity-fed storage water purifier is provided. The gravity-fed water purifier includes a filtration unit for receiving water. The filtration unit includes a housing unit, a first membrane cloth layer, a second membrane cloth layer, and a granular biocidal composition layer disposed between the first and second membrane cloth layers. The first and second membrane cloth layers remove dirt, sand and sediments from the contaminated water, using a depth filtration mechanism. The granular biocidal composition layer removes bacteria and virus from the contaminated water, through fast leaching of silver ions into the water. A single storage container is provided that collects the water filtered by the virtue of filtration unit and gravity. An adsorbent composition is disposed between the storage container and an outlet tap of the storage container.
