Due to the huge increase in population and the growth of the economy, more land is required for housing and living and at the same time food and agricultural goods are needed to be produced to meet the demand of the market. This has resulted in increasing forest encroachment in Thailand and as a result the water source has been affected. Deforestation causes drought and interferes with seasonal rainfall. During the rainy season, without woodland being barriers, water would flow freely down the high grounds causing severe soil erosion and landslides and damage to agricultural plots and to the inhabitants’ properties. Such happening has become more and more intense and frequent on Koh Samui as well as in Suratthani. The speed of the economic growth has also gathered strength, with resulting high increase in land value during these past years. Forest encroachment causes so many problems such as floods, flash floods, shortage of rain.