• Swimming Pool Water – Treatment Processses

    Water Treatment Processes

    Swimming pool water undergoes a number of purification processes in order to get
    it clean. There are different methods available to purify your swimming pool

    Physical Methods

    • Screens – These are used to filter the water and are usually used at the beginning of the purification process. They remove solid particles from the water and their shape depends on which particles they have been designed to filter.
    • Sand Filtration – The filter in this case is made of a multiple layer of sand that varies in size. When the water flows through the sand, solid particles are filtered out. Many particles are not filtered out using this method, so secondary filtration is often required.

    Cross Flow Filtration

    This method uses a permeable membrane to filter out salts and some dissolved matter. There are several membrane filtration methods depending on the contaminant that is to be removed from the water:

    • Microfiltration – This type of filtration is designed to remove very small particles from the water that range in size from 0.1 to 1.5 microns. It is able to filter out suspended matter and some microorganisms.
    • Ultrafiltration – This type of filtration removes even smaller particles from the water that range in size from 0.005 to 0.1 microns. Not only does it remove suspended particles but it can remove other smaller substances such as salts and proteins.
    • Nanofiltration – This type of filtration removes particles from the water that range in size from 0.0001 to 0.005 microns. This means it is effective at filtering out viruses, herbicides and pesticides from the water.
    • Reverse Osmosis – This type of filtration is effective at removing the smallest of particles with a size of up to 0.001 microns. It can remove metal ion particles and dissolved salt.

    Chemical Methods

    There are many different methods of purifying swimming pool water using chemicals:

    • Chemical Addition – You can add certain chemicals to your pool water to combat specific problems. You can add chelating agents to prevent hard water problems. Oxidising agents are effective at killing certain microorganisms and reducing agents can be added to neutralise the oxidising agents to prevent harm to humans. They prevent erosion of purification membranes and neutralise substances such as chlorine and ozone.
    • Clarification – This process removes suspended solids through a number of different processes. Coagulants are first added to reduce ion charges, causing smaller particles to stick together to create bigger ones. These larger particles are then removed through a gravity filter. This method is effective at removing large particles but may not filter out all of them, further treatment may be needed.
    • Deionisation and softening – Ion exchange systems absorb certain anions and cations in order to deionise the water. The cations and anions are replaced by counter-ions until the tank is saturated with ions. The ion-exchanging device then needs to be regenerated with the use of certain chemicals. Water softeners are often used as ion exchangers; they work by removing calcium and magnesium ions from the water, and then replaces them with positively charged ions. This reduces the hardness of the water.


    Disinfectants are used to kill any remaining microorganisms in the water; it is an important process of water treatment as it can prevent pathogenic microorganisms from causing human disease. There are many ways to disinfect your pool water:

    • Chlorine disinfection – Chlorine is capable of killing many microorganisms, but when it reacts with substances that may be present in the water, dangerous carcinogenic chemicals may be formed. This problem can be overcome by using chlorine dioxide which is effective at low concentrations.
    • Ozone disinfection – This type of disinfection works by using oxygen atoms to destroy particles through oxidisation. This is an effective method to kill microorganisms and is not harmful to human health.
    • UV-radiation – This type of disinfection is growing in popularity. It is more natural in its way of killing microorganisms as it uses UV rays to kill germs.

    Biological Methods

    Water purification can also be done biologically using microorganisms such as bacteria. These microorganisms decompose organic matter within the water and therefore reduce the amount of organic suspended matter. There are two types of treatment that use either anaerobic or aerobic bacteria.

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