R-2A AGAR was formulated by Reasoner and Geldreich for heterotrophic plate count of treated potable water. It is recommended in standard methods for pour plate, spread plate, and membrane filter methods for heterotrophic plate counts. Nutritionally rich media support the growth of fast growing bacteria which may suppress slow growing and/or stressed bacteria found in treated water. R-2A agar being low in nutrition, also helps to stimulates the growth of stressed and chlorine-tolerant bacteria at lower incubation temperature and longer incubation period.

for heterotrophic plate count of treated potable water using longer incubation time