Stormwater harvesting and management/Stormwater harvesting system

There are four core steps in stormwater harvesting or collection: "Collection, Treatment, Storage, and Distribution and End Use".

Collection
Stormwater collection is a process of directing water into a storage from stormwater gathering, such as urban runoff. Generally, there are two types, online storages and offline storages. Online storages are a conventional way of acquiring stormwater directly from waterways or drains. For instance, the urban drainage system of channels and pipes conduct stormwater into storages. One inconvenient part of the drainage system is to keep maintenance in case that conduits break and stormwater leaks away. Based on online storages, another drainage system called WSUD is featured. Offline storages require additional facilities to conduct water from waterways indirectly For instance, weirs divert low flows into the stormwater container and contribute to a large part of stormwater catchment for a city.

Storage
There are three factors to consider in terms of storage: function, location and capacity. For function, the planner is responsible for deciding the purpose of the stored stormwater, such as fire fighting, industrial water supplies, farming and irrigation, recreational amenity and flood mitigation. For location, to establish a water tank or an injection system to aquifers above or below the ground should be considered. Besides, choices between online and offline storages can affect the surrounding natural aquatic system and yields different maintenance costs and flood mitigation effeteness. The capacity of a storage relies on the demand of the end use in a particular climate or period.

Treatment
Stormwater treatment is what mostly hinders the progress of stormwater catchment. Water treatment process depends on the intended end use and the catchment equipment, which decides the level of and size of the pollutants to be filtered and removed. Generally, the steps applied for different end uses vary. For instance, as construction uses may not require high-quality water. The water recycling includes only filtration and disinfection. However, for potable uses of higher water quality, the treatment process requires screening, coagulation, filtration, carbon adsorption, and disinfection.

Distribution and End Use
Generally, there are two types of stormwater distribution systems. The first one is open space irrigation systems. The other one is non-potable distribution systems. Some key points are underscored in terms of designing an appropriate distribution system: "Consideration of customer requirements; Adjusting design criteria; Selecting design peak factors; Methods for peak leveling; Controlling distribution non-potable water; Minimisation of bacterial and algal build up; Corrosion risk and so forth".

Water sources become scarce as the population grows. People need to come up with methods to recycle water at the end of its use. For non-potable water purpose of lower water quality, people use stormwater for toilet flushing, gardening, fire fighting, irrigation and etc. For potable water use of higher water quality, stormwater needs to be treated before putting into use. The latter has been rarely used around the world.