This report gives some guidance on how to obtain black-box models of irrigation canal reaches, using system identification techniques. First of all, some general properties of the irrigation canal reaches are deducted, based on the use of the linearized Sain-Venant equations to model the water behavior. Then different aspects of the system identification procedure like the sampling time, the model structure, the experiment design, etc., are studied, in order to avoid possible modelling problems and, in that manner, obtain a good linear model capable to be used in control systems designs. The results obtained in the time domain and the frequency domain show that one can achieve very accurate models, if the system identification procedure is designed with care having in mind the intrinsic properties of the system. The research reveals that it is not convenient to perform a black-box irrigation canal system identification, without having a certain knowledge of the system.