By Amir Yechieli
The water crisis in Israel is mostly due to water mismanagement. One-fifth of the annual rainfall is lost as a result of runoff, particularly in urban areas, via street drains and sewers. This venture is about designing and constructing cost- effective systems to collect millions of cubic meters of rainwater from rooftops. Through rainwater harvesting, many thousands of homeowners, schools, and other public buildings can become less dependent on public water systems during the winter months. On an individual level, this project can provide an alternative to paying for public water and to buying bottled mineral water. On a national level, it can avoid dependence on imported water and desalination, and minimizes the cost and environmental damage from millions of plastic water bottles.
Rainwater harvesting in schools is particularly effective because of a good ratio of collecting area to rate of consumption. Yet, the primary importance of this project is in the teaching of sustainable values and of their practical application, as the system serves as a tool for studying computer science, math, climate and geography.
The innovation behind this rain harvesting system is the use of relatively small containers that are usually refilled about thirty times during the rainy season. Working with a small storage capacity, meant to last for only 7-10 days, ensures high quality water, with minimal space requirements and esthetic problems. The costs of such a system can be recovered in a few years. A system as described above is already operating in twenty five schools around the country and in numerous private homes.
The hardware for the rain harvesting system including drinking water should not exceed 12,000 nis. The hardware for the gray water system should not exceed 3,000 nis. Installation fee depend on the local conditions and on how handy is the customer. Usually if I have to install the rain harvesting system the cost is about 6,000 nis including 1 year warranty. For the gray water installation, depends on local conditions. It may get to several thousand Nis.
A fully operating system if the roof is over 100 sq meter could provide up to 4 month worth of full household consumption + top quality drinking water year round. Just on drinking water the savings could mount to 3000 nis/year.
Gray water use for irrigation could save up to 300 liters /day X 8 month =72 qm/year
Both systems when put in during the construction, through early planning, are chipper to install and more esthetic.