Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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More on Washing Dishes

A reader asks (about rinsing dishes): "If using bleach in bowl 2, can the water be lukewarm or should it be cold?

The answer is that while it can be cold, it is fine if it is warm or even hot. Although the rinsewater used to wash dishes is not intended for drinking, we know from the process for disinfecting drinking water that disinfection is influenced by both the concentration of chemical(s) in the water as well as the contact time of the chemical with any infectious organisms (e.g., bacteria or viruses) in the water. In general, for the purposes of water disinfection, one doubles the contact time if half the concentration of a chemical such as iodine or chlorine is used. If the water is cold, one multiplies the contact time by a factor of 4 to assure disinfection, regardless of the concentration of disinfectant used. Furthermore, if the water is cloudy, one may need to double the concentration of disinfectant. So for cold and cloudy water, one doubles the concentration of disinfectant and quadruples the contact time.

In the study I mentioned in my previous post, the authors noted that the washing-up bowls contained "room temperature" water, but did not specify the precise temperature. If we assume that the temperature of the water was in the vicinity of 70 degrees Fahrenheit, then it is reasonable to suppose that heating the water would certainly not be harmful, and might be helpful, in increasing the disinfecting capability of the rinse water. Having the water be cold might diminish the disinfection effects. Without having any data to support this recommendation, one might allow longer contact time in colder rinse water, based on the principles we follow for disinfection of drinking water.

I note a comment from a reader stating that neither bleach nor detergent are appropriate in the wilderness. I'm glad that someone brought this up, because it represents an important perspective. So, I will address that comment in a future post.

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Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.