This section summarises the appropriate hardware and software tools for treating industrial, domestic or agricultural wastewater. Wastewater treatment may be centralised or take place on an individual level. Wastewater treatment directly influences the quality of water for further use. If wastewater is discharged without treatment, it negatively impacts on the quality of the water available for those downstream. Hence it determines their purification methods, limits the purposes that water can be used for and influences the availability of nutrients for agriculture.