Two alternative configurations or physical systems are used for UV disinfection of small or household water supplies, submerged lamps or lamps in air and mounted above a thin layer of the water to be irradiated. In the units with submerged lamps, the lamps are covered with a protective, UV-penetrable as protection from the electrical hazards associated with water. Water can be treated on a batch basis by placing the lamp in a container of water for several minutes or longer, or on a flow-through basis in a housing or channel, with the water flowing parallel or perpendicular to the lamp(s).
==Construction, operations and maintenance==
==Costs==
Because the energy requirements are relatively low (several tens of watts per unit or about the same as an incandescent lamp), UV disinfection units for water treatment can be powered at relatively low cost using solar panels, wind power generators as well as conventional energy sources. The energy costs of UV disinfection are considerably less than the costs of disinfecting water by boiling it with fuels such as wood or charcoal.
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.
==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.
