Scientists Develop Sunscreen Cover To Stop Lakes And Dams Losing Water

Hyderabad: Researchers in South Africa have developed a thin, floating cover that could significantly cut water evaporation from lakes and dams, offering a possible solution for drought-hit regions.

According to a team of researchers based at the University of South Africa and iThemba LABS, they designed a nanomaterial cover that acts like sunscreen for water. It works by blocking most of the Sun's heat-carrying infrared rays while still letting enough sunlight through to keep aquatic plants and animals alive. The research, led by Daniel Kwasi Kpelgo, was published in the journal Scientific Reports.

Why is water evaporation such a problem?

Water stored in dams and reservoirs often evaporates quickly, especially in hot regions such as southern Africa. As global temperatures rise, evaporation speeds up too, leaving less water available for people, farming, and industry.

Much of this water loss is driven by infrared solar radiation, a type of heat-carrying sunlight. Although sunlight is made up of ultraviolet, visible and infrared light, infrared rays alone account for more than half of the Sun's total energy. This is what heats up water and drives evaporation.

How does the cover work?

The new cover is made by applying an extremely thin layer of material, known as a transparent conducting oxide, onto a lightweight, flexible sheet of plastic. This coating is only a few hundred nanometres thick, with one nanometre equal to one billionth of a metre, making it far lighter and easier to handle than a solid, permanent cover.

In laboratory tests, the cover allowed more than 60 per cent of visible light to pass through, which is important for keeping aquatic life healthy. At the same time, it reflected more than 80 per cent of infrared light back towards the Sun, stopping much of the heat from ever reaching the water.

As a result, water beneath the cover stayed noticeably cooler than the surface of the cover itself, with a temperature difference of up to 10 degrees Celsius during the hottest part of the day. This cooling effect was enough to sharply reduce evaporation.

Results from the tests

During the laboratory experiments, water levels under the coated cover stayed almost the same throughout the test period, showing that very little evaporation was taking place. By contrast, water levels dropped noticeably in reservoirs left uncovered, and also in those covered only with ordinary plastic sheeting.

The cover also floats naturally on water rather than needing a heavy frame or structure to hold it in place. This is because the material is lightweight and water-repellent, meaning water does not cling to its surface.

Advantages over existing solutions

Unlike some evaporation covers that block out most sunlight entirely, this design lets a large amount of visible light through, helping to protect plant and animal life living in the water below.

Because the surface is water-repellent, it was also found to be less likely to develop algae or other natural growth, which could mean less cleaning and maintenance over time for anyone using the technology.

One possible concern with nanomaterials is contamination of the water itself. However, the researchers pointed out that the nanomaterial is not placed directly into the water. Instead, it is fixed as a thin coating onto the plastic sheet, meaning it never actually touches the water below.

According to the study, this work confirms a new method for reducing water evaporation, using a nanoscale coating known as In: SnO2, a transparent conducting oxide, applied onto a flexible plastic base. As well as being extremely lightweight, this coating allows strong transmission of ultraviolet and visible light while remaining highly resistant to infrared light passing through.

This combination brings down both the surface and overall temperature of the water, effectively stopping overall evaporation during a typical day and night cycle.

What comes next?

While this particular study used one specific type of coating, the researchers believe the same basic approach should work with other similar transparent conducting oxide materials, whether passive or active. Further real-world testing would still be needed before the technology could be used on actual lakes, dams, and reservoirs, particularly in regions worst affected by drought and rising temperatures.