What are the steps of water purification to reach a good quality of water ?

A 'Brainstorming' Question indeed! Thanks.

I am in total agreement with Your Meticulous/Constructive sumission Mr.  Ramy Ehab.

Drinking water sources are subject to contamination and require appropriate treatment to remove disease-causing agents. Public drinking water systems use various methods of water treatment to provide safe drinking water for their communities. Today, the most common steps in water treatment used by community water systems (mainly surface water treatment) include:

• Coagulation and Flocculation

  Coagulation and flocculation are often the first steps in water treatment. Chemicals with a positive charge (like :Aluminum sulphate) are added to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc.

• Sedimentation

  During sedimentation, floc settles to the bottom of the water supply, due to its weight. This settling process is called sedimentation

• Filtration

  Once the floc has settled to the bottom of the water supply, the clear water on top will pass through filters of varying compositions (sand, gravel, and charcoal) and pore sizes, in order to remove dissolved particles, such as dust, parasites, bacteria, viruses, and chemicals.

• Disinfection

  After the water has been filtered, a disinfectant (for example, chlorine, chloramine) may be added in order to kill any remaining parasites, bacteria, and viruses, and to protect the water from germs when it is piped to homes and businesses

ASSUMING THAT THE SOURCE TO BE FROM RIVER.

CASCADE AERATION, FLOW MEASUREMENT, FLASH MIXING, FLOCCULATION THAT IS COAGULATION FLOCCULATION,

THEN CLARIFICATION AND FILTERATION, FOLLOWED BY DISINFECTION AND STORAGE.

coagulation, flocculation, clarifier, filtration, disinfection and storage

COAGULATION, FLOCCULATION,

THEN CLARIFICATION AND FILTERATION , DISINFECTION AND STORAGE

it depends on your feed water 

is it city water /brakish water / sea water 

i think its all the same with few changes in  prefiltration steps 

Normally there are three principal stages in water purification:-

1. Primary treatment- Collecting and screening including if required pumping from rivers and initial storage
2. Secondary treatment- removal of fine solids and the majority of contaminants using filters, coagulation, flocculation and membranes
3. Tertiary treatment- polishing, pH adjustment, carbon treatment to remove taste and smells, disinfection, and temporary storage to allow the disinfecting agent to work. Here disinfection is most important.

Design of the processing chain

A water treatment process will generally comprise:   

 * Pre-treatment;    

* Method of treating or main purification    

*finish.

In practice, the chronology of the design will be:    

* Main processing    

* pretreatment   

 *finish.

The lists below can perform a first choice of methods to use.pretreatment processes primary water treatment.   

 * Sand filter: remove large particles, as a first filtration stage   

 * Activated Carbon: elimination of chlorine and organic compounds    

* Softener: remove divalent ions, prevent tartar, both in the pipes in the reverse osmosis    

* Injection acid or basic: pH adjustment  

* Injection of sodium metabisulphite: chlorine removal - often used before a reverse osmosis process   

 * Cartridge filter: removal of suspended particles   

 * Ultrafiltration: Elimination of certain organic substances and colloidal silica    

* Chlorine: iron precipitation, disinfection   

 * Degassing membrane: remove gases (CO2, O2)Selection of the main process    

* Reverse Osmosis: removes particles, bacteria, pyrogens, organic compounds ions    

* Nanofiltration: removes particles, bacteria, divalent ions, reduces the concentration of monovalent ions    

* Ion exchange: removes ions, activated silica, CO2   

 * UV: inactive bacteria and eliminates ozone.   

 * Ozone: virucide2 action eliminates bacteria, precipitates iron   

 * Distillation: pyrogenic and eliminates contaminants    

* Biosolaire purification by microalgae; After installing a driver ( m3 / day) , this technique is  for a capacity of almost EH and m3 per day4, with a positive carbon balance ", which is unique by Laurent Sohier. and could also be tested on landfill leachate.Finishing processes   

 * Heat exchangers mixed bed ion: reduces dissolved solids, residual silica and CO2    * Microfiltration: removes particles and bacteria    

* Ultrafiltration: elimination of bacteria, pyrogenic particles, colloids, some organic compounds   

 * Electrodeionization: reduces dissolved solids, residual silica and CO2

Different techniques are currently being used/adopted to remove the contamination stated above to make water perfect for potable use. The techniques/technologies to be involved are Conventional Sand Filtration, Micron Filtration, Ultra Filtration, Nano Filtration and Reverse Osmosis and some time combination of all these with some physical and chemical aid. 

The diagram above represent the phases of treatment.

it depends on the raw water kind and quality.....river, sea, underground, lack......etc