Baby food formula mixed in the morning and refrigerated throughout the day and reheated and fed at night is a wonderful place for bacterial overgrowth to occur. Many of our baby birds are made sick with this practice. Refrigeration slows bacterial growth. Fresh foods from the grocery are bacteria laden since they have been handled by humans and possibly contaminated by other mammal wastes during storage and shipping. Mice and other vermin can carry bacteria to your food sources.
Water sources are an enigma of their own.
Pseudomonas bacteria is a potential threat to all of our birds on a constant basis. This bacteria loves to grow in your water faucet, particularly if your water lines are PVC pipe instead of copper. I have cultured several aviaries with a Pseudomonas problem strictly due to filthy food and water sources. Water bowls should be above perch level to prevent contamination by fecal material which increases recontamination to your bird and the feces provide organic material in the water bowl for bacteria to grow. Running your tap water for 3-5 minutes before filling water bowls helps flush these bacteria from the faucet instead of filling your bird's water bowl with them.