Pure water is only constitutes of two parts (two molecules) of Hydrogen and one part (one molecule) of oxygen. But pure water as such as is not available in nature.
The water which does not contain any gems hence causes no disease, good to taste and may also be used for cooking and other household purpose is called drinking or usable water.
The water which contain germs or harmful substances that can cause disease or illiness upon consumption is called polluted water.
Today, we are polluting water faster than the nature can clean it up. As per WHO standards, potable water is rare to find. A glass of clean water at glance looks clear but may contain bacteria, virus and harmdul minerals like fluoride, arsenic, lead etc. Excessive dissolved salts can cause serious problems to human health.
In this system harmful Germs / Bacteria can be killed but Hazards chemicals & Virus cannot be rejected.
In this system pores of the candles are bigger than Virus they allow the Virus pass through hence candle filtration is not safe it only removes suspended impurities & gives clean water.
Filter system as both Virus & Bacteria are eliminated in the process, However there are some disadvantages unless the tap water has certain amount of pressure it cannot pass through the filter, beside ultra violet light does not kill Giardia & Cryptosporidia not eliminate hazardous chemicals like lead or asbestos.
This is the most acclaimed water purification system in the world. Here water to be purified is considered a forced out of reveral pressure, this process ensures that very pure water is made available at the end of the R/o procecss.