Fresh water may come from either a surface or ground source and typically contains less than 5 000ppm TDS.

Brackish water contains between 5 000 and 25 000ppm of TDS. Its sources can either be natural fresh water alone or mixed with seawater.  Brackish water differs from open seawater in the biological activity.  Within harbors, bays and estuaries differences can exist in the amount and type of constituents present in the water. The main constituents are the salinity and the silt. Extensive seasonal variation in these is observed.

Potable water is natural fresh water that is made safe for drinking purposes by filtration, extensive treatment and/or disinfection.  World Health Organisation (WHO) issues the guidelines for the allowable limits of various constituents in potable water.  Many countries also have their own standards.

The minerals can be removed by Reverse Osmosis, distillation or Ion Exchange processes.  Water quality is described by specific conductivity.  When the specific conductivity reduces to <0.1μs/cm (Microsiemens Per Centimeter), it is expressed in resistivity (MΩ.cm) – for ultra-pure water.

Cooling water implies that treatment against excessive scaling or corrosion has been applied to.  This may include anything from natural water to seawater and may comprise either an open- or closed- loop system or a once through system.

The feed water make-up for boiler is always softened or demineralised.  Based on boiler pressure it is also subsequently de-aerated  · It may include recovered steam condensate.

This is a general term commonly used to describe water used for process purposes in the industry . This can be from simple filtered water to several times purified ultra-pure water (UPW)

This is a term used to describe water used for general purposes such as washing, flushing, cleaning of process equipment, floor washing and gardening.

By definition waste water is any water that is discarded after use.  Water that results from industrial process or manufacture of goods are classed as industrial waste water. Industrial waste water contains contaminants that are specific to the industry and unit operations.

The waste water from residence and institutions carrying human waste, washing water, food preparation wastes, laundry waste and other waste products are classed as domestic or sanitary sewage.  Waste water from shops/stores and community service establishment, termed commercial wastes are included in the sanitary or domestic sewage category if their characteristics are similar to household flows.

Grey water is the waste water that comes from the laundry, kitchen, bathroom faucets, baths and showers. Black water is the waste water that comes from the toilet and garbage disposal. Thus, municipal domestic sewage is the mixture of grey and black water.

Seawater typically contains about 35 000ppm TDS or 3.5% salinity. The salinity may be reduced due to dilution by rivers with fresh water or concentrated by solar evaporation in others.  Seawater contains some specific impurities such as Boron, Barium, Strontium and marine organisms.