Solar Disinfection of Drinking Water and Oral Rehydration Solutions

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Foreword
Oral Rehydration Therapy: The Revolution for Children
Oral Rehydration Therapy: The Four Simple Technologies
Global Rehydration Therapy: Global Diarrhoeal Diseases Control Programmes
Oral Rehydration Therapy: Causes, Transmission, and Control of Childhood Diarrhoea
Oral Rehydration Solutions: The Practical Issues
Oral Rehydration Solutions: Domestic Formulations
Oral Rehydration Solutions: Disinfection by Boiling
Solar Energy: Fundamental Considerations
Solar Energy: From Sun to Earth
Solar Energy: World Distribution
Solar Energy: A Competitor
Solar Energy: Some Practical Hints
Solar Disinfection Studies: Drinking Water
Solar Disinfection Studies: Oral Rehydration Solutions
Appendix: Source of Information on Diarrhoeal Diseases

Oral Rehydration Solutions

Disinfection by Boiling

The possibility of obtaining clean, safe water for domestic use is rather remote in village settings throughout the developing world. The availability of treated water would be exceptional. Domestic water supplies are therefore expected to be contaminated with microorganisms in varying degrees. Such situations would have a bearing on the purity and safety of the water to be used for the preparation of oral rehydration solutions, and the risk involved in administering contaminated solutions.

It is logical, therefore, for UNICEF to recommend the use of boiled water for the preparation of standard ORS solutions, as is indicated on the labels of UNICEF packets. It is important though to note that the water should be allowed to cool before use. This is necessary to avoid decomposition of the sodium bicarbonate by hot water.

According to the criteria proposed by the WHO Diarrhoeal Diseases Control Programme (document CDDlSER/81.1), a suitable chemical agent to be added to the standard ORS ingredients at the time of packing to ensure decontamination of the reconstituted solution would need to be:

effective against the organisms concerned,
non-toxic to man,
effective in the pH of ORS solution,
non-reactive with the ORS ingredients,
non-reactive with ORS packaging material,
acceptable from the point of view of taste, smell, and colour of the ORS solution,
non-disruptive of the absorption process in oral rehydration, inexpensive .

As none of the chemical agents currently used for the sterilization of water (e.g. chlorine and chlorine compounds) do not meet these criteria, the WHO Diarrhoeal Diseases Control Programme would not recommend their use. In this connection, it should be noted that as a strong oxidizing agent chlorine or its disinfectant compounds (e.g. sodium or calcium hypochlorite) would react with glucose because of its reducing properties . The WHO Diarrhoeal Diseases Control Programme arrives at the conclusion that boiling is an effective method of decontamination of water to be used for the preparation of ORS solutions, but has the following disadvantages:

the difficulty of obtaining fuel and its cost,

the risk that, after boiling and cooling, the water or ORS solution prepared with it may become contaminated during measuring, mixing, handling, or storage,

the (perhaps minor) risk that the users will mistakenly boil the ORS solution after preparation.

On the basis of available information, the following recommendations have been made regarding the preparation of ORS solutions:

ORS solution should be prepared with water made potable by recognized methods (e.g. boiling, chlorination, etc.) in containers washed with such water. This is important because enteric bacteria can grow in ORS solution, and there are as yet insufficient data to show that there is no risk associated with the use of "usual" drinking water;

If potable water cannot be guaranteed, and ORS solution needs to be administered, the best available water should be used;