The Water Cycle

Credits: Biovision-Infonet

Every living creature and vegetation must have water in order to survive.

Only 3% of all water on Earth is fresh water and 68% of the water is frozen ice on the North and South Poles.

All humans and most animals as well as nearly all vegetation can only survive on fresh water free of salt and minerals.

Water for irrigation must also be fresh water and applied sparingly by flood, furrow or drip irrigation, otherwise the irrigated soil will turn saline and unproductive for many years to come.

The other 97% of the water on planet Earth is saline seawater in which whales, fish, corals and plankton flourish. Slightly salty water may be used for watering livestock and other animals, although fresh water is healthier.

Nearly half of all deep boreholes are dry or contain saline (brackish) water with minerals harmful to humans, animals and plants.

Where fresh water is pumped up from very deep boreholes it is called mining fossil water because the water withdrawn cannot be replaced by rains.

Therefore, there are only two sustainable solutions to the world’s increasing demand for water, namely rainwater harvesting and water conservation.

Fresh water sources are replenished in a water cycle through the following activities: 

1. Evaporation is an almost invisible vapour rising from water surfaces.
2. Transpiration is evaporation from vegetation and soil surfaces. 
3. Precipitation from clouds falls as fogs, mists, rains, hails and snow.
4. Rainwater run-off is rainwater running off all kind of surfaces.
5. Drainage is the ability to drain excess water away from catchments.
6. Infiltration is the movement of water into the soil from the surface. 
7. Percolation is the movement of water through the soil to the underground layers.
8. Permeability is the rate at which water penetrates through soils down into the underground water table. 
9. In situ storage is storage of water in the voids between particles of soil and sand.
10.  Subsurface flow is a flow of water in the voids of soil and sand particles.  

Water can be harvested at several stages in the water cycle, such as: 

1.  Fog screens placed on hills, mountains and near the sea for domestic water. 
2.  Gutters attached to roofs for domestic water. 
3. Garlands of stone gutters on rock outcrops for domestic water. 
4.  Soil bunds and trenches on farmland for crops and animals. 
5. Diversion trenches from roads, rocks and hillsides for seasonal flood irrigation.
6. Hand dug wells in shallow ground water to supply water for all uses. 
7.  Subsurface dams, weirs and sand dams to increase the yield of hand dug wells situated along seasonal water courses. 
8.  Boreholes drilled into deep ground water where none of the above options are replicable, although expensive and only 40% may not supply fresh water.  

The quality of water from all these sources can be tested by either a portable testing kit or by a laboratory if the samples can be delivered before deteriorating due to heat over long distances.

Contaminated water may be treated by several methods, such as SODIS (Solar disinfection), boiling, water filters, crushed seeds from the Moringa tree, ultra-violet rays (UV) or artificial chemicals.