Access to safe drinking water is limited in the Mekong Delta region of Vietnam. Rainwater harvesting (RWH) at household level is among the primary sources of drinking water in the region and is widely practiced throughout Southeast Asia. It has recently been increasingly advocated as an alternative or supplemental approach to household water supply. However, relatively little research has been done on current RWH practices and attitudes. We interviewed residents of 619 households in three provinces to understand the current practice of and preferences for rainwater harvesting. We found that rainwater was the most common water source for all domestic activities in the rainy season; however, it was reserved for high-value uses in the dry season. Residents ranked color, perceived safety, smell, taste and reliability of rainwater very highly compared to other water sources. Most households practice daily first-flush and/or boil water before drinking. Storage capacity seems to be a major barrier to RWH providing an adequate supply of domestic water year-round. Because other improved water supplies are not widely available in the rural delta, rainwater harvesting seems to be a promising way to expand access to improved water sources for the residents.