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Reverse osmosis is the finest water filtration method known. This process will allow the removal of particles as small as ions from a solution. It is used to purify water and remove salts and other impurities in order to improve the color, taste or properties of the fluid. R.O. uses a membrane that is semi-permeable, allowing the fluid that is being purified to pass through it, while rejecting other ions and contaminants from passing. This technology uses a process known as crossflow to allow the r.o. membrane to continually clean itself. This is the reason of why an r.o. element can last many years before clogging or need replacement. This water purification process requires a driving force to push the fluid through the membrane, and the most common force is household water pressure or pressure from a booster pump. The higher the pressure, the larger the driving force and efficiency.

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Millions of people are exposed to excessive amounts of fluoride through drinking water contaminated from natural geological sources. As a result, many suffer conditions ranging from mild dental fluorosis to crippling skeletal fluorosis. With the problem continuing to be unrecognized and neglected, guidance is sorely needed.

Clinical dental fluorosis is characterized by staining and pitting of the teeth. In more severe cases, all the enamel may be damaged. In skeletal fluorosis, fluoride accumulates in the bone progressively over many years, leading to stiffness and pain in the joints. In severe cases, it can cause changes to bone structure, calcification of ligaments, and crippling effects.

The World Health Organization's (WHO) publication, Fluoride in Drinking-water addresses this urgent need, providing the latest scientific evidence on the occurrence of fluoride, its health effects, methods to reduce excess levels, and analysis techniques.

Guidance is particularly needed because fluoride is found in all natural waters at some concentration. Low concentrations are good for teeth, but excessive concentrations can lead to debilitating disease, such as skeletal fluorosis, which has devastated some communities. In China alone, more than 10 million people are estimated to suffer from skeletal fluorosis.

While the global prevalence of dental and skeletal fluorosis is not entirely clear, it is known that water is normally the major source of fluoride exposure, with exposure from diet and from burning high fluoride coal also major contributors in some settings. Fluoride occurs at elevated concentrations in many areas of the world including Africa, the Eastern Mediterranean and southern Asia. One of the best known high fluoride areas extends from Turkey through Iraq, Iran, Afghanistan, India, northern Thailand and China. However, there are many other areas with water sources that contain high fluoride levels and which pose a risk to those drinking the water, notably parts of the rift valley in Africa. Many of these areas are arid and alternative sources of water are not available.

This suffering caused by high levels of fluoride can be prevented. Although removal of excessive fluoride from drinking-water may be difficult and expensive, low-cost solutions that can be applied at a local level do exist. Methods outlined in the monograph include: use of crushed clay pots, bone charcoal, contact precipitation, or use of activated alumina (absorptive filter). It is important that local authorities consider the causes of fluorosis carefully and choose the best and most appropriate means of dealing with excess fluoride exposure taking into account the local conditions and sensitivities.

Fluoride in Drinking-water is one out of a series of WHO monographs, which address the management of other chemicals in drinking-water, such as arsenic or cyanotoxins.

Sourced from World Health Organization
21 November, 2006  Geneva