Engineering structures require precise planning before its construction to provide economical and sustainable service. Due to long service life and high initial investment costs, preliminary planning is of particular importance for water structures. The size and type of the water structure to be projected is highly related to the amount of water consumption rate. The determination of water consumption rate which is considered to be realized in the future provides an important contribution to the construction process of these special structures. However, in some regions it is difficult to estimate the water demand because of inadequacies or missing records in previous water consumption rates. Classical prediction methods cannot perform well with limited number of data. Gray Prediction Model is one of the most commonly used methods when there are few records. In this study, annual water consumption rates of the province of Istanbul were estimated by using Gray Prediction Model which is a contemporary method. The results of the Gray Prediction Model was tested with the help of statistical error criteria and it was found out that this method gives satisfactory results in hydrology area even if number of data is limited.