Generally a source of water begins from hill regions. The water vapor becomes fog when it reaches the higher levels of the atmosphere. That is how the clouds are appearing. When the clouds are gathering to the hill regions the humidity of them absorbs by the plants of natural forests. Generally these plants in the natural forests of hill regions have a lot of specific features for absorbing the moisture. The absorbing of moisture is happening well in the night. When this is happening regularly the ground becomes wet. There is a limit of water holding capacity in the soil. When the moisturizing exceeds the water holding capacity excess water is being secreted to the low down from the upper hills. By gathering the excessive water which has been secreted the natural ponds are appearing. Most of rivers are beginning from natural ponds in hill regions.