It should be paid attention to minimise side effects, since poorly designed and managed systems can lead to soil erosion, soil instability and local floods. Water harvesting techniques increase the water availability, yet the climatic variability can not be completely compen­sated. Years with extremely low precipitation still threaten the production, and torrential rainfalls can often lead to destructive runoff. Large storage tanks may be required in areas where the dry season is long. In addition, the rainwater may be contaminated, so that extra care should be taken when the collected rainwater is used as drinking water. The success of water harvesting projects is often based on farmer’s experience and their willingness to adopt and accept the techniques (Prinz, 1999).