Water harvesting is almost 4000 years old: it began in the Bronze Age, when desert dwellers in the Middle East smoothed hillsides to increase rainwater runoff and built ditches to collect the water and convey it to lower lying fields. Archaeological findings and historical descriptions show that water harvesting played an important role in supporting a flourishing agriculture in many regions. A wide variety of hydraulic structures have been introduced during many centuries to make the land productive irrespective of its restrictive natural conditions. Presumably millions of hectares of land in dry areas, where rainfall is low and erratic in distribution, were once cultivated with water harvesting techniques, but many causes have brought a steady decline. Namely the preference of larger irrigation schemes and social changes like the migration of manpower are responsible for the common neglect of these techniques. But since water harvesting represents a sustainable method of providing non-costly water and improving the productivity of land that suffers from inadequate rainfall, the interest in these systems has increased during recent decades.