The following table defines some of the more technical terms used in this
document.
| Aerobic |
describes a process requiring oxygen to work |
| Alluvium |
deposits brought down by rivers. Initially, alluvium is
often a clay, sand or fertile marl but, in time, can compress into a
frequently imperveous rock |
| Anaerobic |
describes a process where oxygen must be excluded |
| Aquifer |
a permeable layer of rock which has water flowing within
it, forming a water table |
| Flash distillation |
a method of purifying water by pumping it at a medium
temperature into a partial vacuum chamber, causing it to "flash" into steam
which is then condensed. It can be done over a number of stages and the
heating of the water may be solar. |
| Hard water |
water rich in calcium or magnesium salts which form a
scum with soap |
| Heavy metal |
there is no formal definition, but is generally
considered as metals with an atomic weight of more than about 44 |
| Hydrology |
the study of underground water, its flow and its
exploitation |
| Igneous rock |
rock which is formed from some volcanic action, e.g.
basalt, pumice, pillow lava |
| Ion |
an electrically charged particle, dissociated when a
salt is dissolved in water, e.g. when table salt dissolves, it dissociates
into positive (cation) sodium ions and negative (anion) chlorine ions. |
| Ion exchange |
a method of water purification whereby dissociated ions
from salts in water are replaced by hydrogen and hydroxyl ions which combine
to form pure water. |
| Metamorphosis |
a process where the structure or chemical nature of a
rock changes with age, pressure or temperature e.g. limestone changing into
marble |
| Microorganism |
any living matter of microscopic size, including
viruses, bacteria, amoebae etc. Although many microorganisms in water are
dangerous to human health when drunk, even fatal, there are many others
which are not. |
| Osmosis |
the passage of water from a purer quality to a saltier
quality through a semi-permeable membrane, such as organic tissue. |
| Phreatic |
describes water within an aquifer, which may be pumped
to the surface by a borehole |
| Phytoplankton |
the smallest vegetable microorganisms which form the
lowest member of an aquatic food chain. |
| Potable |
describes water which is both palatable and safe to
drink |
| Reverse osmosis |
a method of water purification whereby water containing
impurities (such as salt) is forced through a semi-permeable membrane by
high pressure: requires much energy. |
| Sedimentary rock |
rock which is formed by the compression of deposited
silt, sand, organic matter or shells, e.g. chalk, limestone, sandstone |
| Soft water |
water low in calcium and magnesium hydroxides and
carbonates but which may contain other salts |
| Vadose |
describes underground water flowing through fissures in
impermeable rock |
| Water softening |
a method whereby calcium and magnesium ions, dissolved
in hard water, are replaced by sodium ions. This is not a purification but a
change in chemical composition to prevent scum formation in the presence of
soap. |