Surface water and groundwater sources exist across most of Samoa, although their distribution is not uniform. The older volcanic terrain of the Fagaloa and Salani volcanics have a clay cover that results in impermeable strata, and therefore surface runoff. These older volcanics and associated surface water courses are mostly located on the eastern and southern halves of both the Upolu and Savai’i islands. The younger volcanics of the Mulifanua, Lefaga, Puapua and Aopo lave flows have little or no soil coverand allow the infiltration of nearly all rainfall. These lavas are highly permeable, allowing also rapid groundwater flow to the sea. These younger volcanics are along the north-west Upolu and Savai’i regions and coincide with the dominant distribution of coastal springs and good groundwater sources (MNRE, 2013; SOPAC, 2007). Upolu island has about 15 more or less perennial rivers, while Savai’i island has about 4 perennial rivers (MNRE, 2013). River flow is good during the wet season whereas in the dry season, ephemeral rivers and streams begin to dry up and perennial river systems experience low flows (MNRE, 2013). Rainwater harvesting has only been reported to be practiced to any extent in the Falealupo Peninsula of north-west Savaii, where a combination of the highly permeable Puapua volcanics and the relatively isolated geographic peninsula appear to result in saline groundwater and no surface water courses, giving the local populace no alternative but to use rainwater harvesting. This has been practiced since 1993. There is no known use of non-conventional sources of water in the country (SOPAC, 2007).

(Food and Agriculture Organization of the United Nations (FAO))