Water activity (a_w) is important indicator for food quality, safety and storage stability, where a_w is directly related to bacterial growth, especially when a_w is above 0.90. Water activity in relation to bacterial counts of dehydrated bovine milk may have been studied extensively, while no report has been available for the correlation between a_w, pH and Escherichia coli survival in powdered caprine milk (PCM). The objectives of this study were to determine a_w, pH and Escherichia coli counts of PCM, and evaluate correlations among these parameters at 4°C and 22°C for 0, 2, and 4 mo storage. Three different lots of commercial whole PCM were purchased at a local retail outlet and divided the total amount of each lot into 2 equal portions to assign them to 2 treatment groups: control and E. coli inoculated groups. Ten grams of the experimental PGM samples were inoculated with 50 μL of E. coli K12, and control samples without inoculation of the pathogens were subjected to the temperature and storage treatments. Water activity was measured by AquaLab a_w meter (cx-2; Decagon Devices, Pullman, WA). All experimental PGM samples were also analyzed for E. coli counts according to the manufacturer’s procedure (3M Center, St. Paul, MN). Results showed that a_w values were significantly (P < 0.05) reduced, where mean a_w for 0, 2 and 4 mo storage were 0.266, 0.251, 0.243; 0.291, 0.266, 0.219, respectively. No differences in pHs were found between 2 temperature groups, while pHs were slightly higher at 2 mo storage. Mean E. coli counts of 4 and 22°C at 0, 2 and 4 mo storages were: 5.01, 4.16; 3.43, 1.85; and 3.77, 1.48 cfu/g, respectively, indicating that E. coli counts significantly (P < 0.01) decreased during 4 mo storage. E. coli counts were significantly correlated with a_w, having r = −0.857 at 4°C and −0.771 at 22°C, respectively. Correlations between levels of pH and a_w at both temperature treatments were also negatively correlated. It was concluded that E. coli counts of the powder goat milk were negatively correlated with levels of water activity as the storage time advanced.