UV units to treat small batches (1 to several liters) or low flows (1 to several liters per minute) of water at the community level are estimated to have costs of 0.02 US$ per 1000 liters of water, including the cost of electricity and consumables and the annualized capital cost of the unit. On this basis, the annual costs of community UV treatment would be less than US$1.00 per household. However, if UV lamp disinfection units were used at the household level, and therefore by far fewer people per unit, annual costs would be considerably higher, probably in the range of $US10-100 per year. Despite the higher costs, UV irradiation with lamps is considered a feasible technology for household water treatment.
==Field experiences==
'''The Power of UV Light'''<br>
During the summer of 1993, Gadgil and a graduate student investigated the effectiveness of UV light and whether it was economically feasible. "We were completely amazed," he says. "Using the simplest engineering, we could disinfect water for half a cent per ton. That's shockingly cheap. You could disinfect one person's drinking supply for a full year for a couple of cents."
From his experiences in India, Gadgil knew that any system would have to require little maintenance and not take for granted basic infrastructure like electricity and water pressure. The system he and his student built, later named UV Waterworks, is remarkably simple. In a compact, enclosed box, a UV lamp is suspended above a shallow pan. Water runs into the pan under the force of gravity, where it is exposed to the UV light, then into a holding tank. The only power that is needed is about 40 watts to power the light; this can come from a car battery. The system can disinfect four gallons of water a minute, killing 99.999 percent of bacteria and viruses. This produces enough clean water to serve more than 1,000 people.
Water Health International, the company founded to bring the technology to market, now makes several different versions of Gadgil's disinfection system, for small and large applications, for emergency use, and for locations that also need to filter out silt and other large contaminants. Prices start at about $1,500.
UV Waterworks systems have been used in India, South Africa, the Philippines, Honduras, and other countries. Since 1998, the Mexican government has installed about 100 in Guererro, a state on the Pacific in southwestern Mexico. The results have been very positive. In the summer of 2000, Gadgil reports, people from Water Health International returned with stories and data showing a dramatic decline in the incidence of diarrhea among children and adults. And preventing deaths and illness are just the most visible effects of purifying water—it also protects children from stunted physical and mental growth. "This is the kind of story that really makes my day, really makes me happy," Gadgil continues. "It makes me feel good when I get up in the morning."
==Acknowledgements==
* [http://www.who.int/water_sanitation_health/dwq/wsh0207/en/ Managing Water in the Home: Accelerated Health Gains from Improved Water Supply]. WHO, 2002.
* [http://web.mit.edu/invent/www/ima/gadgil_bio.html Courage: Ashok Gadgil.] From the book: Inventing Modern America: From the Microwave to the Mouse. David E. Brown. MIT Press.
