The prevailing winds carry this warm, moisture-bearing air over the continents, where the topography causes it to rise, cool and form clouds. Under the right atmospheric conditions, the clouds become supersaturated and the excess moisture is released as precipitation in the form of rain, snow or hail.

Once the precipitation reaches the earth’s surface, it will tend to wet the surface and begin to infiltrate the soil if possible. However, the soil is not always able to absorb the water, especially during heavy rainfall periods. This water begins to flow along the line of the steepest slope over the ground surface and feeds the natural drainage network (ditches, streams and rivers), a process which is referred to us as run-off. If the surface is highly impenetrable, as in the case of urban areas, or zones with low permeable rocks, run-off may appear almost instantaneously, in moderate and heavy rainfall events.

Some of the precipitation water is taken up by plants and transpired back to the atmosphere. Thus only a relatively small portion of the precipitated water remains in the soil surface. This subsurface water moves towards the earth’s centre under the force of gravity.

The water is percolated downwards until it reaches the water table of the underlying aquifer. After reaching the water table this water then continues flowing in the aquifer in a down gradient direction until it discharges to the surface as (springs or seeps) or flows into the ocean. Occasionally the downward flow is interrupted by an impermeable layer, the water then flows laterally until it can continue its downward flow to the water table.

An interesting fact regarding water on Earth is that 98% of the water on Earth is salty and is in the oceans. The total amount of fresh water is only 2%. Of this 2% only 5% is visible water in our streams, rivers, dams and lakes. The remaining 95% is groundwater, or as the Minister of Water Affairs, Mr Ronnie Kasrils dubbed it “Our Hidden Treasure.”