There are several types of systems used in the households of developing countries to treat drinking water. The best technologies for home- or office-based water purification systems in developing countries combine filters, which clarify the water, with chlorine or bromine biocides, which effectively kill germs. Iodine is suitable for short-term, emergency use only and results in water that has an offensive odor and taste.
 
Other systems for treating drinking water include:
• Reverse osmosis (RO), a separation process that uses pressure to force water through a membrane that allows only pure water to pass to the other side. RO is one of the fastest-growing technologies for treating water because it helps neutralize and remove many contaminants, including some minerals and chemicals such as fluoride, iron and arsenic. However, RO has a number of downsides: it requires adequate water pressure and often a reliable power source (both of which are often unavailable in developing countries), its membranes can fail, it requires regular maintenance and checkups, and, worst of all in a world of scarce resources and diminishing water supplies, it rejects and wastes a high percentage of the source water.
• Ozone systems, which are effective and sophisticated, requiring generators and injectors, pumps and pressure tanks, and filtration systems. Because of their cost, complexity and electricity requirements, they are out of the price range of most people in developing countries.
• Ultraviolet (UV) light systems, which use ultraviolet light to disinfect water and kill germs. They require electricity, thorough prefiltration of the water so the UV beams can penetrate and get to the germs, and high-quality, appropriately sized UV lamps, as well as regular maintenance. UV systems are out of the price range of most people in developing countries.
• Desalination, a process by which excess salt and other minerals are removed from water. It is an expensive system, consumes massive amounts of electricity, works slowly and produces distilled water that tastes bland to most people. In addition, RO-based desalination is not reliable as a “purifier.”
• Ceramic filters, which vary in effectiveness. At the high end, ceramic filters remove cysts and bacteria, but most ceramics don’t remove bacteria, and some are of such low quality they may not even remove cysts. In India, low-end ceramic filters just filter out dirt, making the water clearer, but not safe to drink. Most water treatment systems use ceramic filters, carbon filters or other filtration media at the front end to remove dirt, sediment and cysts.
• Boiling water, which is a popular way for consumers in developing countries to purify their water, but it requires a lot of energy (compressed natural gas, kerosene or electricity). Plus, it is time-consuming for consumers to boil and then wait for water to cool down before drinking. In some parts of the world, people have to chop down trees and burn scarce resources to boil water, often in areas with poor ventilation, which causes health problems.
• Iodine, a sister halogen to chlorine and bromine. Iodine kills germs, but its residual in the water leaves a bad taste and odor. Most importantly, iodine is not healthy for long-term use. Many products using iodine resins will scavenge or polish the iodine residual from the product water but fail to remove odorless and tasteless iodide, which presents a significant health risk with long-term intake.
• Pitcher systems, such as Brita. Pitchers use filtration to clean water and make water taste better, but they do not kill germs or purify water.
• Water softeners, which typically remove minerals but not germs.