Water supply systems typically take raw water from a source

and perform filtering and treatment processes before delivering

the water to the distribution system. There are a number of

potential physical and chemical processes at each step,

governed by the quality of the raw water and the regulatory

environment that the water supply system must comply with.


Raw water sources include:



  • Ground water, called aquifers or well fields depending on where you are in the world. These are natural layers of water found deep underground, bounded by impervious substrates of rock or clay that traps the water. They are supplied by rain filtering through the earth and underground rivers from elevated surrounding areas. The raw water may be at pressure, evidenced by natural springs bubbling to the surface or may require pumping using submersible pumps.

    • Due to depletion of aquifers in many areas aquifer levels have been dropping requiring significantly deeper wells and higher energy to lift the water to the surface.

    • Aquifer water is often very clean and pure, requiring little if any treatment although salt infiltration as a result of over-extraction allowing brackish water into the aquifer and contamination from surface industries is problematic.



  • Surface water

    • Rivers provide a ready source of water but are subject to seasonal flow variation and short term contamination events like storm run-off after heavy rainfall.

    • Lakes are also a great source of raw water and can provide storage to cover seasonal variations in water demand. The lakes also allow sediment to settle out of the incoming river and stream water.



  • Brackish water and seawater desalination

    • With most readily available fresh water sources already in full use and water demand increasing, more diverse water sources must be evaluated for use. In low rainfall countries (e.g. the Middle East) and in areas where climate change is reducing annual rainfall (e.g. Australia) desalination and water reclamation is very common.


  • Re-use water

    • Almost 75% of potable water delivered to consumers is returned to the utility as wastewater. This can be a valuable source of water, creating either new potable water, or more commonly as a source of irrigation or industrial water. Singapore leads the way in water re-use, using energy and chemical intensive processes.





Not all raw water requires treatment beyond basic mechanical screening to prevent visible object entering the water supply system, for example New York city does not treat its water, relying on protected catchments in the Catskill Mountains to ensure high quality raw water.


Typically however most utilities perform a variety of mechanical and chemical processes, including:



  • Water intake

    • Screening to remove leave, sticks, floating rubbish etc.

  • Pre-treatment

    • Sedimentation basins to allow fine particles to settle out

    • Coagulation using chemicals like alum to form floc blankets, essential clumping together fine particles in the water so they become heavy enough to settle out


  • Treatment

    • ​Filtration using fine sand, anthracite or other filtering medium

    • Micro-filtration using fine strands of porous material to filter out particles

    • Reverse osmosis or nano-filtration for brackish water/seawater

    • Activated carbon stages to remove taste and odour issues or remove colour

    • Chemical processes like CO2 or Lime to correct pH or precipate out calcium


  • Purification (once the water is optically clean and clear) 

    • Chlorine or Chloroamine added to sterilise water

    • UV sterilisation passing water past banks of intense UV light

    • Ozonation using ozone gas to kill any harmful organisms


  • Public Health additions, mainly fluoride for oral health are not specifically part of water treatment

Note: UV and Ozone only kill organisms already present in the water, Chlorine and Chloramines also protect against future intruding organisms in the distribution system to the customers tap.


  • Smart Water Interfaces include:

    • Real-time data or data logging from raw water sources like rainfall gauges, stream level data, or water quality

    • Programmable Logic Controller (PLC)-control-based systems at the water treatment plant for monitoring and controlling all stages of water treatment from raw water collection to screening, filtration and chemical addition, providing a vast variety of data and control in real-time

    • Instruments used to measure parameters in the water, (e.g. pH, turbidity, chlorine residual)





Water treatment is often regarded as one of the greatest public health initiatives in history, resulting in a very significant reduction in disease and avoidable deaths around the world. Although not available to everyone on the planet, there is a steady growth in water treatment in newly industrialised nations who are observing the same benefits.





For smart water systems a control system using Programmable Logic Controllers (PLCs) or a Distributed Control System (DCS) at the water treatment plant is often necessary as this provides the foundation for data collection, storage and analysis. The controls system also provides the path for control outputs to change operations in response to optimisation analytics.