China Water Week｜How hard does humanity fight for water? Scientists' water-saving "black technology"

March 22nd to March 28th is China Water Week. On March 22nd, at the main venue of the "Water Saving China Tour·Beijing Chaoyang" theme promotion event in Chaoyang, Beijing, the "Top Ten Classic Cases of Water Saving in China in 2024" were officially released, which included both management innovations and technological advances. In addition, what other methods do you know about water conservation?

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01 Cover the reservoir with "sun protection clothes"

In August 2015, 96 million black hollow high-density polyethylene balls were slowly spread across the Ivanhoe Reservoir in Los Angeles, as if the reservoir was covered with a thick layer of “sun protection clothing.” These small balls, 10 centimeters in diameter, float on the water surface and can effectively block sunlight, reducing evaporation by about 1.15 million cubic meters per year[1].

However, experts have calculated that it will take at least two months to two and a half years for these black plastic sunshade balls to provide the desired protection. Moreover, the production of these plastic balls themselves requires 250,000 to 2.9 million cubic meters of water (depending on the thickness of the ball wall).

Image generated by AI

In addition, these black plastic balls may hinder the oxygen exchange of water bodies, causing hypoxia in water bodies and affecting the survival of aquatic organisms. Moreover, these plastic balls may gradually age and break during long-term use, posing a potential threat to the ecological environment of reservoirs. However, scientists are not discouraged by this. They are actively developing biodegradable materials and look forward to creating a "sunscreen clothing" for reservoirs that is both practical and environmentally friendly in the future.

02Zero -energy “desert water dispenser”

Liquid fresh water exists not only in rivers, lakes and seas, but also in the form of mist suspended in the air. In the extremely arid Lima, Peru, people hang a special net on the hillside to capture mist, allowing tiny water droplets to condense on the net and then flow down the river to be collected in pipes. According to statistics, a net can collect 300 to 400 liters of fresh water a day[2]. Although it cannot be drunk directly, it can be used for washing clothes, bathing, washing vegetables and boiling for cooking. The most amazing thing is that this device does not require electricity and can only work in a cycle based on the temperature difference between day and night. It can be called the most energy-saving "desert water dispenser". Today, this fog-catching net has been widely used in Peru, Bolivia and some areas of Colombia.

Image source: WaterSeer

In 2017, the University of California, Berkeley, developed an air-water extraction device called "WaterSeer". This device is very simple to use. It only needs to be inserted into the ground, and then the temperature difference between the upper air and the part below the ground is used to produce moisture, just like the condensed water produced in an air conditioner. After testing, WaterSeer can collect up to 37 liters of water per day [3, 4]. With it, people in areas where groundwater is severely scarce can use air to produce safe and reliable drinking water, and no longer have to worry about drinking water.

03 "Seafood Miracle" in the Desert

Most of Israel's territory is covered by the Negev Desert. As early as 1970, locals drilled in the desert to find water sources and discovered geothermal brine. This water is not only hot, with an outlet temperature of about 40°C, but also has a higher salinity than drinking water. After experiments, scientists have developed a method for multiple utilization of geothermal brine. They combine agricultural planting with aquaculture, first introducing geothermal brine into greenhouses to keep crops warm. After consuming part of the heat, the cooled water is then graded and flowed into different fish ponds to breed different species of fish suitable for different living environments[5]. Here, every drop of water is used to its full potential, truly realizing the efficient and circular use of water resources.

A drone shot of a cold-water fish breeding base in Wenquan County, Xinjiang. (Photo by Li Qiang, Xinhua News Agency)

Xinjiang in my country has also recently become popular for its seafood. In recent years, through technological innovation and comprehensive utilization of water resources, people have used the abundant underground saline-alkali water resources in the desert to build breeding ponds in the desert, regulated the water quality to simulate the marine environment, used a circulating water system to keep the water clean, and rationally adjusted the lighting, ventilation and other environmental conditions according to the growth needs of seafood. A variety of seafood products such as crabs and prawns have been raised in canyons and saline-alkali lands, creating a fishing legend in the desert Gobi.

04 Artificial intervention to get water from the ocean

Sometimes, people will change the direction of water resources through artificial intervention to rationally allocate water resources. However, changing the direction of the river requires not only the courage to change the world, but also accurate planning and design and strong financial support. It is not easy to succeed. For example, the Dead Sea, which is famous for its high salinity, is still dropping at a rate of about 1 meter per year. In order to save the Dead Sea, some scholars have proposed the idea of ​​pumping water from the Red Sea, desalinating it for local use, and then injecting salt water into the Dead Sea. However, because this project is very expensive and may damage the ecological environment of the Dead Sea, it has not been implemented to this day.

The game between humans and water is a collision between technology and nature. Behind every technological innovation lies a respect for nature. Only by finding a balance between efficient use and ecological protection can we truly protect the source of life.

References:

[1] Zhang Mengran. Los Angeles Reservoir Experiment Shows that Using Sunshade Balls to Reduce Water Evaporation Is Not Feasible [N]. Science and Technology Daily, July 20, 2018.

[2] CCTV News. Talk about this magical fog-catching net [N]. CGTN Global Information Broadcast, May 19, 2024.

[3] WaterSeer can extract water from the air [N]. China Civil and Commercial Law, Issue 12, 2016.

[4] https://offgridworld.com/waterseer-provides-endless-supply-pure-water-thin-air/

[5] Hao Yu. Desert Fishpond[J]. Nature Exploration, Issue 5, 2022.

Author : Ma Zhifei, senior geological engineer , member of the Geological Society of China , winner of the Natural Resources Excellent Popular Science Book Award

Reviewer : Xu Kui, Associate Professor, Department of Water Resources and Hydropower Engineering, Tianjin University

Planning : Zhai Guoqing

Produced by : Science Popularization China