One of innovation to tackle flood-prone areas with little water absorption is geopolymer. Addition with heavy metal accumulator microbial formulation can decrease carcinogens in fly ash. The procedure is begin with microbial isolation, starter made with subcultured microbes transferred to media with addition As2O3 and Cr2O3 to see effectiveness. Prototyping with mixing fly ash, rice husk ash, alkaline medium and microbes starter. The result shown that arsenic rate can diminish until 90% in geopolymer.