The Study On Roof Rain-water Utilization

China is shortage of water resources. To sovle the problem of lack of water resources, rainwater usage has been paid more and more attention. It can be used not only in the place where water shortage is serious, with plenty of water resources in the region is also feasible. Rainwater Utilization project involves many factors。The main factors of the impact of the use of rain water are analyzed in this study, then makes optimal design and reasonable assessment for these factors。Roof area is very important to the choice of rainwater drainage systems and utilization programmes. When the roof is large in size, the drainage system can be established through technical and economic comparison. As the gravity flow of the drainage system has greater potential, the system's design do not have to consider raising the return period. Siphon system is the ultimate use of the potential energy systems, so the systems design return period should be increased, but not too much. The more Roof larger, we can collect the more rainwater to reuse. we Should handle the convergence issues of rainwater reuse and drainage system.Roof rainwater contaminated material is COD and SS. the concentration of pollutants are associated with the size of roof materials,seasonal and temperatures. For the most economical use of water, consideration should be given on the appropriate discarding of the early rain. Disposable flow of 1 ~ 2 mm can meet the requirements. We can fulfill the disposable flow through disposable devices.Water treatment process should be based on the requirements quality of reuse. Conventional water treatment process coagulation - precipitation - filter - disinfection will be able to meet most of the water quality requirements. For special requirements of the reuse, it can be ultrafiltration membrane filters, and other requirements to meet water quality. The rainwater use and landscape should be combined to maximize the overall effectiveness.The scale of the storage tank is critical to the optimization of rainwater reuse system. The size of the tank place great impact on the collection efficiency, investment and costs. Optimization design should aim at the the largest ratio of cost-effectiveness to find out economical scale. We can obtain the storage pool volume through the use of reasonable step in various thickness of the rainfall, Accordingly, econimical scale obtained by the curve of the ratio between the costs and efficiency. Rainwater utilization project is a systematic project involving economic, technological, environmental, social, and many other factors. Evaluating the use of rainwater should reflect all aspects of the comprehensive optimal. With the Analytical Hierarchy Process ,we can establish a multi-objective comprehensive evaluation of the integrated multi-level hierarchical structure model. With experts and policy makers'subjective judgement and objective data together, the modle gives out quantified description of the programme, then the use of rainwater is reasonable evaluatted.