R2A Agar is used for the enumeration and cultivation of bacteria from potable water in a laboratory setting. R2A Agar is not intended for use in the diagnosis of disease or other conditions in humans. R2A Agar was developed by Reasoner and Geldreich for bacterial plate counts of treated potable water. R2A Agar is a low nutrient medium, and in combination with a lower incubation temperature and longer incubation time, stimulates the growth of stressed and chlorine-tolerant bacteria. Nutritionally rich media support the growth of fast-growing bacteria, and may suppress slow growing or stressed bacteria found in treated water. When compared with Tryptone Glucose Yeast Extract Agar or Plate Count Agar (Standard Methods Agar), R2A Agar reported improved recovery of stress and chlorine-tolerant bacteria from drinking water systems. R2A Agar is recommended in standard methods for pour plate, spread plate, and membrane filter methods for heterotrophic plate counts.