Since ancient times people and their governments have taken on large and creative projects to increase their local water supply.
Ancient farmers in the Middle East conceived a way to bore horizontal tunnels, known as qanats, into nearby hills to intercept groundwater and let it flow by gravity down the tunnels to their farms and settlements. The Romans are noted for the magnificent aqueducts they built to transport water from distant sources to their cities. In more recent times, huge engineering projects such as the Los Angeles, California, and Colorado River Aqueducts have been built to transport water from the Owens Valley, northern California, and the Colorado River to parched southern California. In China, which also had monumental water transfer projects in ancient times, another large canal is being built to move water from the humid south to the arid and populous north of the country.
There are other ways to increase supply besides water importation. These include:
This can be done on a small scale, one household at a time, using a rain barrel to catch water that falls on the roof. It can also be done on a community scale, using a paved catchment or other large impervious area that drains to a larger storage basin. Under suitable climatic conditions of alternating rainy and dry seasons, rainwater harvesting can provide a significant boost to water supplies.
Surprisingly, many experts agree that weather modification in the form of cloud seeding appears to have frequent success in wringing additional moisture from clouds that pass over an area. It is difficult to measure the effectiveness of cloud seeding in a controlled experiment, but sophisticated and careful modeling, along with many observations, appears to bear out this conclusion. One downside is that a downwind community might complain that upwind cloud seeding robs clouds of moisture that might otherwise be destined for the downwind community.
In some areas with severe water scarcity, there are few rain clouds, but moisture can still be wrung out of the air by capturing fog. One example is Namibia, the desert coastal country mentioned previously. Rain clouds seldom form, but fog frequently rolls in from the ocean. Devices have been installed that are basically large nets on which fog droplets are captured, delivering their moisture to storage vessels. In one community in Namibia, such a fog harvesting project yielded up to 2,500 liters of clean, fresh water on a good day. Similar projects have been used in other foggy areas such as the Andes and the Himalayas.
Removing salt from seawater or brackish surface or groundwater can be an effective means of supply enhancement. According to the International Desalination Association, there are over 18,000 desalination plants worldwide, and they are increasing in number by about 10 percent every two years. The main disadvantage of desalination is that it requires a large amount of energy, and is therefore quite expensive. Other disadvantages include the problem of disposing of the concentrated salt brine that is a by-product of the process, and the need for proximity to the ocean or a source of brackish water.
As we have discussed previously, many communities and individual water users seek a solution to water supply enhancement by increasing rates of groundwater withdrawal. With today’s sophisticated drilling rigs and high-capacity pumps, it is relatively easy to pump groundwater at a rate that greatly exceeds the rate of aquifer recharge. We have seen how this is like drawing down the principle of a savings account, and is in effect robbing water from future generations. Nonetheless, groundwater mining continues to be one of the principle forms of supply enhancement. USA Today, citing a study by the University of California Irvine and the Jet Propulsion Laboratory report that half the world’s 37 largest aquifers are being depleted by groundwater mining. When water levels drop enough to make it economically infeasible to withdraw more groundwater, or when the aquifer goes dry, the forced reductions in groundwater pumping will add significantly to future water scarcity.
© Colorado State University