現代的都市環境多為不透水表面，高度的不透水表面率不僅造成都市雨水逕流問題，並導致都市高溫化現象，破壞都市生態平衡。為了解都市環境中的透水性能，本研究以臺南市為例，依據臺南市土地使用分區及公共設施用地匯整為九種分區，再利用抽樣的方式對181個基地進行不透水表面率的調查與分析，來做為都市環境透水性能的解析依據。結果顯示各類分區之平均不透水表面率為：住宅區86%、商業區100%、工業區92%、公園綠地36%、學校68%、機關用地91%、其他公共設施用地81%，其結果比一般文獻上對於國內都市不透水表面率的預估值偏高許多，且以建蔽率對於不透水表面率的影響最為顯著。同時，本研究採用都市人為開發區的不透水表面率來客觀地評估都市中整體的不透水狀況，結果顯示的臺南市人為開發區之平均不透水表面率84.02%，遠大於臺南市平均不透水表面率46.72%。足見臺南市都市的人造空間，已對自然的透水環境造成巨大傷害。

　　　　　The urban environment nowadays is consisted of impermeable materials. This high percentage of impervious area (IMP) not only causes the phenomenon of urban runoff, but brings about high temperature in urban and destroys the urban ecology. In order to understand the performance of permeability in the urban environment, the Tainan city was selected as the population and 181 building sites were sampled from 9 zones defined by the land use and zonings of this city. After the investigation and analysis of the method of permeability on the land surface and IMP in each site, the result shows that the value was 86% in residential area, 100% in commercial area, 92% in industrial area, 36% in parks, 68% in schools, 91% in government organizations and 81% in public facilities. The values are much higher than official records in the past and are related with the ratio of building coverage. Furthermore, the index of "IMP of urban" and "IMP in developed area of urban" are brought up to evaluate the impermeable characteristic of the city. After the calculation of each index, the value of "IMP in developed area of urban" (84.02%) is much higher than "IMP of urban" (46.7281%). It shows that the artificial materials on the land surface of urban environment in Tainan have damaged the original permeable environment violently.