What happens to the raw water until it gets into our glass? Advanced water purification methods

Previously, you could already read about natural and anthropogenic water contaminants. Now we present those physical and chemical water purification methods which guarantee safe drinking water supply. Water treatment can be very varied in different regions due to the diversity of chemical composition of raw water and the degree of pollution.

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The first step of water treatment is the removal of floating material, this process is mostly done  by physical methods. In case of surface water, immediately upon withdrawal, grids are used to block floats, so that they cannot damage the system of the waterworks. This is followed by the removal of large, well-settled materials using sand traps. Activated carbon filters can be used as well to filter out  smaller particles that cause undesirable smell and taste.

There are contaminants which, due to their small size, cannot be effectively removed from water by the former processes. In this case, settling can be intensified chemically by the addition of chemicals (most commonly iron and aluminum sulfate). As a result of adding chemicals, the small contaminant substances form macro-flakes, so that they can be settled. There are also several types of  membrane filters which can physically remove most organic and inorganic contaminants. Such processes include nanofiltration and reverse osmosis.

Raw water often contains toxic or unhealthy ions as well, such as  iron or manganese. These ions are in a dissolved, reductive state in groundwater. After withdrawal they are oxidized and precipitate, so they subside in pipelines. To avoid that, we can make oxidation more efficient with aeration or added oxidizers. The resulting precipitate can be removed by filtration or settling. We can also use the method of ion exchange, mainly for water softening (it means the removal of Ca and Mg ions) or pH balancing.

Raw water must be treated against infections and microbiological pollution as well. Disinfection is usually made by chlorine, ozone, or even UV light.