Harvesting Water

In parts of the world where there are heavy rains for a few months per year, then an extended dry season, managing water is a challenge. This is particularly true if there is a large urban population in such a region. Typically this challenge is met through construction of large storage dams and reservoirs. But there is another way.

For thousands of years urban dwellers have constructed cisterns to harvest runoff. But for the last fifty years or so, the conventional wisdom has been to ignore the potential of cisterns, and focus on dam building. Whether or not dams are a valid solution to water management, the ancient practice of building water storage capacity in the form of decentralized cisterns is making a comeback.

In a newly launched superblog “network of networks,” GoingOn.com, an ABC News Network reporter Dinesh Rawat has just posted news from India, where in Rajasthan, government policy is turning to cisterns to harvest water. Here it is:

“Rajasthan is likely to make water harvesting structures compulsory for all types of buildings and plots in urban areas, earlier this rule was mandatory only for plots of 300 square metre or more. Houses on all types of plots and buildings, including government, semi-government, educational institutions, commercial and industry buildings, will have to construct water harvesting structures. A bill to this effect will be introduced in the next session of Vidhan Sabha.

Local bodies minister Pratap Singh Singhvi said the rule has been critical in arresting the fast depleting ground water level. This rule, he hoped, would help in recharging the ground water. Singhvi said those buildings, which do not have water harvesting structures, would not be given water connections. The civic bodies at the time of map clearance of the building will deposit a security amount for building water harvesting structures. If the builder fails to build it, then the civic body would utilise the security deposit to construct it.”

In our article “India’s Water Future,” at the bottom of the story there is a chart showing water usage in India and elsewhere. Indians on average consume 470 cubic meters of water per year – Europeans on average consume 605. This would equate to a cistern nearly 8 meters per side for every person in every building. But because this per capita quantity includes water used for agriculture and industry, this is a misleading statistic.

According to ITT Industries Guidebook to Global Water Issues, the average urban dweller can enjoy an excellent lifestyle on just 150 liters of water per day, which is only 55 cubic meters per year. This would equate to a cistern less than 4 meters per side for every person in every building, a far more practical size. Moreover, cisterns don’t have to completely replace water distribution systems, nor is their storage necessary during the rainy season.

Taking these factors into account, cisterns of modest size can decisively solve the challenge of providing adequate water to urban areas that receive torrential rain for part of the year, but on balance experience water scarcity.

Categorized | Buildings
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