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A Program for Safe Drinking Water through Solar Disinfection

Global Resources Institute has initiated a SunWater Program to promote the use of solar disinfection as a process to produce clean drinking water for the millions of people who suffer from diarrheal and other water-borne diseases due to unclean drinking water.

The program is directed toward two, often overlapping, populations: people in developing countries who lack access to clean drinking water in every day life and people in areas at risk for natural or man-made disasters who are likely to be suddenly confronted with unsafe drinking water.

Over 1 billion people lack access to safe drinking water. Over 2.2 million people die of water borne diarrheal diseases each year, 90% of them children, mostly in developing countries. In addition, in the decade ending in 2003, more than 2.5 billion people were affected by earthquakes, floods, hurricanes and other such events. The lack of clean water was often a major concern in such disasters.

Much of the illness and death caused by the lack of clean water can be prevented by the use of solar disinfection which is a very simple and virtually free method of water purification. Solar disinfection uses the ultraviolet (UVA between 300 and 400 nanometers) in sunlight to disinfect bacteria, viruses, and some cysts in water to provide safe drinking water. It has been shown to be effective against a wide range of pathogens including those causing cholera, typhoid, dysentery, cryptosporidiosis, giardiasis, numerous diarrheal diseases, and polio. Water placed in glass or PET plastic bottles and placed in daylight is disinfected in four to five hours in direct sunlight or a full day in cloudy weather. A common practice is to expose water for a full day to be used the next day. Where bottles are not available, clear plastic bags, shallow pans, or "plastic puddles" made from sheet plastic or tarpaulins can be used.


Plastic bottles on a rack of black corrugated steel roofing on a roof top in Lumbini, Nepal

Plastic Bags in a Field Setting

A Plastic Puddle in a Field Setting

Since solar disinfection does not use any chemicals, electricity, or other equipment, it is a readily available method that can be used in emergencies, disasters, or daily life wherever clean water is not accessible. It can also be used as an interim measure in those places where other means of water purification are being planned. Solar disinfection can be presented as components of formal and informal education programs and placed within the agendas of many development activities. The key points of solar disinfection can be found at Key Points.

Solar disinfection was practiced in India centuries ago when water was exposed to daylight in shallow pans and was rediscovered and researched in Lebanon by Aftim Acra and others beginning in the 1970s. UNICEF published a report of their work and recommended its use. <>. Since that time solar disinfection has been extensively researched and promoted by Dr. Martin Wegelin and others at the Swiss Federal Institute for Environmental Science and Technology. They have carried out laboratory studies and field studies in many developing countries. <>. A group at the Royal College of Surgeons in Ireland has done research into the basic process of solar disinfection, its effects on various pathogens, and its effectiveness in field studies. On World Water Day in March 2001 the World Health Organization endorsed solar disinfection as one of two "Immediate Solutions for Persistent Problems" of water quality and urged its promotion. <>.

In 1999 with support from US-AEP/NASDA, Global Resources Institute conducted field studies and training in Lumbini, Nepal on solar disinfection in collaboration with the International Buddhist Society (IBS) and its medical clinic. The clinic reported an 80% decrease in diarrhea among 5,000 villagers who used solar disinfection for nine months. Clinic Report (About 50,000 children die each year in Nepal from diarrheal diseases.) The villagers gave solar disinfection the local name of "Gham Ko Paani" ("Sun Water" in Nepali), which GRI has adopted for its international program.

Sine its initial work in 1999, GRI has continued to introduce solar disinfection in Nepal with its most recent training held in Kathmandu in October 2005. GRI has also provided materials to organizations working in Kenya and Haiti.

Most applications of solar disinfection make use of PET plastic bottles which are typically used for bottled water and soft drinks. Questions have been raised regarding chemical breakdown of PET plastic bottles when exposed to sunlight and possible contamination of the water with carcinogens or other harmful chemicals. Tests by the Swiss Federal Institute for Environmental Science and Technology on PET bottles have shown that although some breakdown may occur on the outside of the bottles, harmful by-products are not present in the water inside the PET bottles.

Plastic bottles become scratched and dirty with use and may become cloudy with age, rendering them less useful for solar disinfection. The lifetime of a bottle in daily use is found to be approximately four to six months. Since a family of six may use 12 to 16 bottles of water a day, when cycling them every other day a family may require as many as 32 bottles. Even in a village of modest population this can create an environmental burden over time. Since PET bottles have value for recycling, a recycling program should be a component of any solar disinfection plan for a neighborhood or community.

Since the effectiveness of solar disinfection has been tested, demonstrated and proven in the laboratory and many field projects, the present task is to raise awareness of the value of solar disinfection and to promote its use in emergencies, disasters and daily life wherever clean water is not available. In addition to targeting people in developing countries who lack access to clean drinking water on a daily basis, recent disasters have underscored the importance of making solar disinfection a part of the public's storehouse of preparedness information before disaster strikes. To attempt to introduce a new concept to a disorganized and traumatized populace can be a daunting task. The public should know about solar disinfection in the same way that it knows about the use of tourniquets. This is especially important in areas where people are subject to recurring monsoon floods, hurricanes and other natural disasters.

In order to spread knowledge of solar disinfection and to promote its use, the SunWater Program has three long-term objectives: to develop educational and training materials on solar disinfection, to build partnerships with agencies and organizations to disseminate the information, and to work for the implementation of solar disinfection programs in developing countries and disaster-prone areas.

Areas of GRI's current and future educational efforts include developing posters, booklets for use in schools and non-formal education, training flip books, background materials for trainers and decision makers, video and audio materials, materials on establishing a solar disinfection infrastructure including the recycling of plastic bottles and website development. Posters presenting the basics of solar disinfection are available at SunWater Posters.

For further information about Global Resources Institute's Sun Water program, to offer suggestions, to discuss ways of partnering with GRI, and to engage in a dialogue regarding solar disinfection, please contact Peter Moulton, Ph.D., Executive Director at <>

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  last modified January 2006