Using a classic example of a three-hectare freshwater reservoir on the slopes of Table Mountain with approximately three million cubic litres of water, the value of water lost to evaporation is best explained.
If the reservoir is not continually augmented with fresh water, evaporation will basically drain the entire reservoir of all water within a year.
Preventing open water bodies from losing water to evaporation is a challenge all over the world. Forward-looking cities have sporadically explored water evaporation prevention systems with varied success, but to date this has been done with limited levels of success only, and more often than not, not repeated elsewhere.
Facing a catastrophic drought, the City of Cape Town, Water and Sanitation, has invited technology proponents active in the water sector to present water-saving/purification technology options for evaluation to the City’s Economic Development and Innovation Directorate.
Unfortunately, only 2% of Cape Town’s fresh water demand comes from dams and reservoirs which fall under the city’s jurisdiction, and, at 2%, hardly makes an impression on the demand volume.
Nevertheless, and given the volume thereof running into millions of kilolitres, 2% of the water demand is an enormous amount of water.
And, given the critical drought, it could be argued that every drop counts. Why have the authorities not investigated evaporation prevention solutions sooner?
The supply of water to the City of Cape Town from large dams falls under the administration of the national government, and all decisions regarding those dams lie with Pretoria.
Although the Department of Water and Sanitation (DWA) supports evaporation prevention, the dams under their administration are simply too big to cover up.
Also, at this stage DWA concerns itself with construction and hard interventions in ensuring storage capacity and water transfer capability and maintenance.
The City of Cape Town, however, is now in the process of probing the advantages and disadvantages of investing in water evaporation technology.
Easier said than done: covering open water dams remains a huge challenge, given immensely strong wind and wave action and harsh sunlight.
Agriculture and mining can benefit from research.
Water evaporation prevention technology in South Africa was developed for use by irrigation farmers and coal mines facing severe water shortages that hampered production and further development.
While dealing with the effect of invasive alien plants on water loss in catchments, rural conservation entities such as SCLI initiated the development of evaporation prevention, given the huge cost of clearing catchments compared to the cost-benefit advantage of preventing loss through evaporation.
By preventing vast amounts of water from evaporating, dam levels are stabilised and more water can be released for downstream users so river systems and aquatic life keep healthy and alive.
The SCLI is a public platform for landowners and land managers with an interest in and water stewardship and the eradication and control of invasive alien plants.
The initiative is supported by the Table Mountain Fund, a subsidiary of environmental group WWF SA.
Meiring works for The Southern Cape Landowners Initiative