Although untreated wastewater contains different types of harmful pollutants, treated wastewater can be used for many purposes. The usage of treated wastewater depends on its treatment level (e.g. reuse of treated wastewater in irrigating vegetables that are eaten raw, such as lattice, requires no pathogen contents).
Treated wastewater is a valuable resource that should be used as much as possible. Accordingly, treated wastewater is used to irrigate different types of plants such as trees, flowers, grass and even vegetables. Also, treated wastewater can be used for recreational activities such as artificial lakes that can be used for different sport activities. Moreover, treated wastewater can be used to recharge groundwater to increase its capacity of fresh water. Additionally, treated wastewater may be used in urban areas for flushing the toilets and in industries including aquacultures.
Usage of treated wastewater should be applied with care to avoid environmental pollution. There are cases of groundwater and surface water pollution that occurred because of the usage of treated wastewater. The reason is that treated wastewater may contain high levels of nitrogen and phosphorus that may be good for plants but at the same time may cause nitrification and eutrophication of water bodies. In some cases, treated wastewater may contain high levels of heavy metals.