The combination of prediction method is the hottest one of the topics in Forecasting Science.The basic meaning of the combination forecast is the prediction model using the weighted average combinations of two or more for a model.Combination forecast of the key is to determine the combination coefficients or weighting factor.This paper introduces combining forecasting method of water consumption discharge from history data of the past seven years.This paper establish the mathematical model of water consumption from multiple perspectives: regression forecasting model, seasonal forecasting models, gray forecasting GM(1,1) model and combining forecasting model.Combining forecasts produces better accuracy than any one of the single models.Such forecast provides important general guidance to short-term and long-term plan of water consumption.As w ell as, with its robustness and accuracy, the optimized compound forecast model is extensible in the forecast o fconsumption of other resources.