Blog

The main water cycle starts, of course, with rain falling on the earth, most of it making its way to the sea by means of rivers, although the journey may be delayed by lakes. Water derived from the river/lake system is called surface water. The balance of the rain soaks into the ground and becomes held in underground aquifers (porous rock strata), from which it may eventually emerge as springs, if it has not been abstracted as ground water. From a purification point of view, the two types
of water have very different needs. Ground water is essentially clean of suspended material, by virtue of its prolonged filtration by porous rock, but it is heavily loaded with dissolved matter (hard water) of many different kinds, and has the mineral taste accepted by many as the taste of pure water. Surface water, by contrast, has very little in the way of dissolved salts (soft water), but is frequently loaded with fine suspended solids and colloidal matter, with a lot of dissolved organic material, which gives the water a marked brown colour and an unpleasant taste.

Water abstracted for domestic or industrial purposes will come from whichever source is the most convenient, which usually means the nearest, so the raw water quality will be decided by the geology at the point of abstraction (for example,
mainly soft from the impervious rocks of northern and western Great Britain, and mainly hard from the limestone hills of south-eastern Great Britain). The treatment processes required to convert raw water to fresh are thus largely dictated by the
nature of the source of the raw water.

These treatment processes involve the purification of the raw water to a state fit to drink, which state is also good enough for many other domestic, commercial and industrial uses. Some end uses require a higher degree of purity, but the final result
of the use of standard or high purity water is the same, namely the production of a large quantity of contaminated wastewater, sometimes highly contaminated. This then leads to the second major part of the water cycle, the need to treat the wastewaters adequately to permit them to be returned to the earth, in river, lake or sea.

That describes the main water cycle, relying on ‘ fresh ’ water sources, but the great majority of the earth’ s water is that in the sea, which is far too salty for human or animal use, or for irrigation, and so must be desalted before it can be used for
drinking or irrigation. The desalination of salty waters is a well established technique, but is an expensive one and very energy intensive. It is thus employed either where energy is cheap or there are no other sources of water. The cost of production from salt water is so much greater than that from fresh water that the incentive for water conservation is correspondingly greater, and the waste treatment component of the water cycle is of lesser importance in the total expenditure.

The global water situation is steadily worsening because of polluted groundwater, rivers and lakes, over-enriched and dirty seas, and water shortages within the growing populations of the less developed world. Water is, of course, essential if
humans and animals and plants are to survive, and a major problem is that most people in the developed world take both hot and cold water for granted, and often squander it without reflection.

There is hardly any raw water treatment in the less developed world, and the standard of treatment is low in many other areas. Suitable technology does exist to achieve a satisfactory standard of water production, and, with the advent of greater political awareness of the problems and stricter environmental legislation, there are many opportunities to improve the world ’s water supply.

Look for more information, please click here.