In many arid areas with water scarcity then utilising surplus water including waste water re-use is of concern.
A surplus water resource is usually surplus because it cannot be easily and economically utilised. If you are going to use it in irrigation then it has to be available when it is needed in irrigation. If it is a groundwater resource then it is surprising that it is not already being utilised. But, then you need to look at the environmental and water balance imapcts over the whole basin not just your local city. If it is a surface water resource there may be no advantage to storing it in surface impoundments just to lose it in evaporation. It may be best to use it in groundwater recharge.
47,783 m3/month is obviously an average - it could irrigate about 12 ha but you need to know the monthly and annual pattern of surplus over a period of years before you can start considering what to do with it.