In today's mature seawater desalination technology, economy is an important factor that determines its wide application. In China, "high cost and investment cost" has been regarded as the main problem that seawater desalination is difficult to use boldly, but in fact, it is a "recognition" problem.

At present, there are three common ways to take fresh water in the world: underground water, remote water transfer and seawater (brackish water) desalination. As an important open source measure, the exploitation of underground water has small quantities and low costs, which are attractive advantages. However, the exploitation of underground water is greatly limited by the resource conditions. Moreover, due to the excessive exploitation of underground water in many areas for many years, underground funnels have been formed, resulting in the tilt of houses, and even causing environmental hazards such as seawater backflow. The exploitation of underground water has been restricted.

At present, the project investment cost and the indirect economic loss of the water diversion area are not included in the calculation of remote water diversion, but only the daily operation cost and management cost, which is quite different from the real cost. In fact, in addition to the huge investment, the water diversion project will also occupy a large amount of arable land, and there are also problems such as the environmental hazards of the area being diverted. For example, the Yellow River Diversion to Qingdao (Island) Project, which covers an area of 62000 mu, will also cause ecological environmental problems such as the cutoff of the Yellow River and vegetation damage, and the damage to the ecological environment is incalculable economically. The Luanhe River Diversion Project implemented in the 1980s still costs about 2.3 yuan per cubic meter today, and there is a government subsidy of 0.9 yuan from the water price of 1.4 yuan for Tianjin residents. Experts predict that after the implementation of the South-to-North Water Diversion Project, the Yangtze River will flow to Beijing, and the comprehensive cost will be more than 5 yuan per cubic meter based on the current constant cost, and even some experts predict that it will reach 20 yuan per cubic meter. According to data from the United States, the cost of long-distance water transfer will exceed that of seawater desalination if it exceeds 40 kilometers.

For seawater desalination, energy consumption is the key to directly determine its cost. Over the past 40 years, with the improvement of technology, the energy consumption index of seawater desalination has been reduced by about 90% (from 26.4 kwh/m3 to 2.9 kwh/m3), and the cost has been greatly reduced. At present, the cost of seawater desalination in China has been reduced to 4-7 yuan/m3, while the cost of brackish water desalination has been reduced to 2-4 yuan/m3. For example, the cost of seawater desalination in Tianjin Dagang Power Plant is about 5 yuan/m3, and the cost of brackish water desalination in Cangzhou City, Hebei Province is about 2.5 yuan/m3. If the desalinated concentrated brine is further used for salt production and chemical extraction, the desalination cost can also be greatly reduced. As for some productive process water, such as boiler water in power plants, due to high requirements for water quality, it needs to be re-treated by tap water. At this time, its comprehensive cost will be much higher than the one-time treatment cost of seawater desalination. It can be seen that the unit cost of seawater desalination, especially brackish water desalination, is actually very competitive if the policy factors such as government subsidies are put aside and the economic and technical aspects are analyzed.

Cost comparison of several fresh water acquisition methods Unit: yuan/m3

Average cost of water intake mode

Limited exploitation of groundwater

Remote water diversion from Luan to Tianjin: 2.3 yuan/m3 (direct cost)

South-to-North Water Transfer: 5-20 yuan/m3 (average water price to Beijing)

Seawater desalination: 4-7 yuan/m3 (comprehensive cost)

Bitter water: 2-4 yuan/m3 (comprehensive cost)

In China, due to the influence of the planned economy, there has been no benign water price formation mechanism for a long time. The price of tap water has seriously deviated from its value. The government bears huge subsidies. The price of tap water is generally low. At present, the price of tap water is generally 1.5-2 yuan/cubic meter. With the continuous progress of desalination technology and the emergence of industrial scale benefits, the cost of seawater (brackish water) desalination will be lower and lower. In October 2000, Premier Zhu Rongji stressed at the South-to-North Water Transfer Symposium that "we should establish a reasonable water price formation mechanism, gradually raise water prices substantially, and give full play to the role of price leverage". With the increasing shortage of fresh water resources, water-saving measures have been introduced in various cities, and the use of tap water has been limited and the price has been increased beyond the standard. It can be predicted that in the near future, on the one hand, the cost of seawater desalination will continue to decrease, on the other hand, the price of tap water will continue to rise, and the two will become closer and closer. The price of tap water will even be higher than the cost of brackish water desalination, and the cost of seawater desalination will be solved. The solution of the cost problem will greatly promote the wide application and industrialization of seawater desalination.