Making every drop count
Glossary
catchment. The area from which a river, stream, lake or other body of water receives its water.
disinfection. Physical or chemical treatment to destroy harmful microorganisms. The disinfecting properties of sunlight are due to ultraviolet light.
global warming. An increase in the average temperature of the Earth's surface. Global warming is one of the consequences of the enhanced greenhouse effect and will cause worldwide changes to climate patterns.
groundwater. Water that is found beneath the surface of the ground, usually in porous rock known as an aquifer. The top of this groundwater is called the water table. For more information see What is groundwater? (Connected Waters, University of New South Wales, Australia).
membranes. A thin sheet of material that is permeable to substances in solution.
microfiltration. A membrane filtration process which removes contaminants from a liquid by passage through a microporous membrane. The pore size of a typical microfiltration membrane ranges from 0.1 to 10 micrometres. Microfiltration can remove many pathogens from water including Giardia, Cryptosporidium and large bacteria.
osmosis. The movement of water between two solutions, separated by a membrane that permits the free passage of water but prevents or slows down the passage of dissolved substances. The water moves more rapidly from the less concentrated solution to the solution of a higher concentration than in the opposite direction. Reverse osmosis is the movement of a solvent in the opposite direction from osmosis. Pressure – usually 5 MPa - 20 MPa – is applied on the high concentration side of the membrane, forcing the solvent through a membrane to a solution of lower concentration. Pure solvent is obtained on the other side. The membranes used for reverse osmosis do not have pores: rather, separation takes place in a polymer layer of microscopic thickness. For more information see How reverse osmosis works (How Stuff Works, USA).
potable. Water that is fit for drinking purposes.
sewage. Liquid and solid waste carried in sewers.
ultrafiltration. Is a type of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane allowing only the passage of small molecules. Ultrafiltration only differs from reverse osmosis and microfiltration in the size of the molecules it retains.
ultraviolet. The term for electromagnetic radiation that has a wavelength just beyond the violet end of the visible spectrum. Ultraviolet disinfection can be used to kill microorganisms in water. For more information see FAQs about ultraviolet water disinfection (Triangular Wave Technologies, USA).
Posted August 2006.