An estimated 1 billion persons in low-income countries do not have access to improved drinking water. Chlorine, a useful water treatment agent, is less effective in turbid water, and lacks a visible effect, limiting its acceptability. A product incorporating precipitation, coagulation, flocculation, and chlorination technology (combined product) to reduce microbial, organic and heavy metal contaminants in water was evaluated. The combined product's microbiological efficacy in Guatemalan villagers' households was evaluated. One hundred randomly selected households from four neighboring Guatemalan villages were enrolled. Three groups received the combined product and either the Centers for Disease Control (CDC) water storage vessel, a covered bucket with spigot, or no vessel. One group received chlorine bleach and the CDC water storage vessel, and one group no intervention. Household water samples were collected for 4 weeks and Escherichia coli, chlorine, and turbidity levels were measured. Potable water was defined as having less than one E. coli per 100 ml. Eight (8%) baseline water samples were potable. Follow-up water samples were more likely to be potable than control samples (combined product and traditional vessel 83%; combined product and CDC vessel 92%; combined product and covered bucket with spigot 93%; chlorine and CDC vessel 92%; versus control 5%). Among combined product users, 98% reported improved water clarity compared with 45% of chlorine bleach users (p<0.0001). The combined product technology improved water potability as effectively as chlorine bleach; improved water clarity could motivate more persons to effectively treat their water.