It is of great significance for the long-term planning and allocation of Nanjing water resources to analyze the current situation of Nanjing water consumption, make reasonable prediction of Nanjing water consumption and master the future water demand. The analysis of water consumption in Nanjing from 2009 to 2019 showed that industrial and agricultural water consumption accounted for a large proportion of total water consumption in Nanjing, which played a crucial role in the change of total water consumption. The combined model of grey GM(1,1) model and Elman neural network was used to forecast the water consumption of all districts and the total water consumption of Nanjing. The results show that the grey Elman neural network model has a good prediction effect on the total water consumption of Nanjing City from 2009 to 2019. The relative errors of the forecasts were all less than 3.5%, and the average relative errors of the predicted results over the years were 1.55%; The relative error of the forecast results is less than 8.5% in the forecast of the water consumption of all districts in Nanjing in 2019. The model used in this paper can accurately predict the water consumption of Nanjing, which is of great significance to effectively control the regional water consumption and realize the principle of "four water and four determinations".