Nanomaterial Blanket Offers a High-Tech Solution to Water Loss in African Dams

Water stored in dams and reservoirs for human consumption often evaporates, particularly in hot regions such as southern Africa. Rising temperatures accelerate this process, leaving less water available for communities, agriculture, and industry. Daniel Kwasi Kpeglo, who recently completed a PhD in physics, explains his laboratory research into an innovative design: a thin, floating nanomaterial cover that could be placed over lakes and dams like a protective blanket. The concept works by limiting the infrared heat from the sun that reaches the water, thereby reducing evaporation. He also outlines the practical hurdles that must be overcome before the design can be tested in real-world conditions.

Why is reducing water evaporation so important?

Reducing evaporation essentially means wasting less of the water we have already collected. The premise behind my research was straightforward: if we can preserve more of the water we have stored, we lessen the pressure to locate new water sources.

This is especially relevant for Africa, where water held in dams and lakes plays a critical role in water security, food production, and resilience against drought.

How does the nanomaterial cover prevent evaporation while allowing sunlight to pass through?

My research centered on a novel nanotechnology-based floating cover for water surfaces. The concept is comparable to placing a carefully engineered shade over the water. I investigated whether an existing nanomaterial could be positioned on water to function as a selective filter for sunlight. The study aimed to determine, for the first time, whether a nanomaterial could address evaporation by permitting most visible light to pass through while blocking the heat-carrying infrared radiation.

This nanomaterial is created by applying an extremely thin layer of a transparent conducting oxide onto a lightweight, flexible plastic sheet.

This cover helps maintain a cooler water surface. Allowing some sunlight to pass through is essential, otherwise aquatic plants and animals would perish. My cover permits useful light to enter while shielding the water from heat.

In our experiments, the cover allowed more than 60% of visible light to pass through on average, while reflecting more than 80% of infrared light back into the atmosphere. Consequently, the water beneath the cover stayed significantly cooler than the upper surface of the cover. The water was 10°C cooler during the sunniest part of the day, minimizing evaporation.

There is another important advantage. Because this cover is lightweight and hydrophobic (water does not cling to its surface), it can float directly on the water without requiring a heavy support structure.

In our laboratory experiments, the water level remained essentially unchanged under the coated cover during the test period, indicating that very little water was evaporating.

In contrast, the water level dropped noticeably when the reservoir was left uncovered or covered only with a standard plastic sheet.

What other methods prevent evaporation, and why is this approach superior?

Floating or suspended covers, shade cloths, wind barriers, aquatic plants, and natural materials like palm fronds have all been used to reduce water loss. Some researchers have explored chemical treatments to create a sunscreen for water, but these typically block all sunlight, whereas our approach targets only infrared radiation.

We believe our new design is superior because nanomaterials are exceptionally lightweight. The transparent conducting oxide is applied as a coating only a few hundred nanometres thick over a flexible, lightweight plastic sheet. To put this in perspective, one nanometre is one billionth of a metre. This makes our cover far easier to handle than a heavy, permanent structure.

Second, because it allows most visible light to pass through, it has the potential to reduce evaporation without entirely cutting off sunlight from the water below. This is vital for reservoirs that sustain aquatic plants and other forms of life.

Third, the coated surface is water-repellent, and during testing we found it was less prone to developing layers of algae or other biological growth. This could translate to less cleaning and maintenance over time.

While there is a potential concern about nanomaterial contamination, our design does not place the nanomaterial directly into the water. Instead, it is used as a thin coating fixed onto a plastic sheet, keeping it from touching the water itself.

What needs to happen next?

We have only tested this in a laboratory-scale water reservoir using an artificial light source designed to simulate sunlight. We tested various light conditions and distances from the water surface, comparing an uncovered reservoir, one covered with ordinary plastic, and one covered with the coated material. The results consistently showed that significantly less water was lost when the coated cover was used.

The next critical step is to transition from the laboratory to real-world application.

This is what would need to happen:

First, large-scale field trials are necessary to evaluate how the cover compares with existing solutions in terms of cost, durability, maintenance, and overall environmental impact.

A field test would help answer questions that laboratory experiments cannot. How does the material perform under real sunlight, wind, rain, and fluctuating temperatures? How long will the cover last? How will it behave on moving water? What would it cost to manufacture and install over a large reservoir?

Second, in a natural dam or reservoir, the cover would need to be attached to a floating system to prevent water currents and wind from displacing the sheets.

Third, to deploy the nanomaterial on real dams, a scientific study must be conducted on durable, UV-resistant materials, such as polycarbonate. This is because prolonged exposure to ultraviolet radiation can degrade certain plastics, making them brittle, prone to cracking, and breaking down into small fragments. Before this cover can be launched, we need to ensure the material can withstand years of sun exposure while maintaining its floating performance.

Daniel Kwasi Kpeglo, PhD in Physics | Materials Science & Computational Physics | Scientific Computing, University of South Africa

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