Coastal water receives a large number of pollutants from urban area which have a potentially adverse effect on water quality and aquatic ecosystems. The sources of the discharge of such pollutants are categorized into two types: point and non-point sources. Point source means pollutant sources which are easily identified facilities discharging pollutants to the environment. Factories, housings and sewage treatment plants are included in this category. In many countries, the quality of the discharged water from these point sources is regulated by laws and is controlled by a wide range of treatment technologies. Diffuse sources of pollutants such as vehicles and urban surface materials are called non-point sources. Non-point source pollution occurs with rainfall or snowmelt. The water from rain or snow dissolves the atmospheric pollutants, washes off the pollutants on the impervious surfaces and finally flows into rivers, lakes and coastal waters. Naturally, the non-point source pollution is difficult to control, since the water is irregularly discharged. The monitoring or sampling of such irregular water discharge requires special devices and/or incurs high labor costs. The source responsible for the pollution is often unclear, not least because the water runoff itself is a natural phenomenon and the pollutant sources are diverse; responsibility is thus difficult to assign. As such, the significance of non-point source pollution in the water environment tends only to be recognized after the controlling system of the point sources has been spread well in the society.