Glossary of terms used in the chemistry and purification of water.

Absorption – A process by which a substance is taken up chemically or physically in bulk by a material (absorbent) and held in pores or interstices in the interior.

Activated Carbon – A highly porous form of carbon used for sorption of organics and removal of chlorine and chloramine.

Adsorption – Adherence of molecules, atoms and ionised species of gas or liquid to the surface of another substance (solid or liquid) as the result of a variety of weak attractions.

Anion Exchange Resin – An ion exchange resin with immobilised positively charged exchange sites, which can bind negatively charged ionised species, anions.

Azeotrope – A blend of two or more components with equilibrium vapour phase and liquid phase compositions that are the same at a given temperature and pressure.

Bactericide – A chemical or physical agent that kills bacteria.

Biocide – A chemical or physical agent that kills microorganisms.

Biofilm – A layer of microorganisms enclosed in a glycoprotein polysaccharide matrix, which are adherent to each other and/or to surfaces.

Carbon Fines – Very small particles of carbon that may wash out of an activated carbon bed.

Cartridge – A pre-packed disposable container for housing a water purification resin, media or membrane.

Cation Exchange Resin – An ion exchange resin with immobilised negatively charged exchange sites, which can bind positively charged ionised species (cations).

CFU/ml – Colony Forming Units per milliliter. A measure of viable microbial populations.

Colloid – A stable dispersion of fine particles in water that have a typical size less than 0.1 μm. Colloids containing iron, aluminium, silica and organics are commonly found in natural and potable waters.

Concentrate – The liquid containing dissolved and suspended matter that concentrates on the inlet side of a membrane and flows to drain.

Condenser – The stage of a distillation system that removes sufficient heat from a vaporised liquid to cause the vapour to change to a liquid phase.

Conductivity – Conductivity is the reciprocal of resistivity. For water purification systems, conductivity is usually reported as microSiemens per centimeter (μS/cm) at 25°C.

Degassing – The removal of O2 and CO2 from water, usually by transfer across a hydrophobic membrane. CO2 is removed to increase down stream ion exchange capacity.

Deionisation (DI) – Removal of impurity ions from water. Usually used to refer to ion exchange – see Ion Exchange.

Distillation – A purification process that takes advantage of changing the phase of a substance from liquid to vapour and back to liquid usually at the boiling temperature of the substance, in order to separate it from other substances with higher or lower boiling points.