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The investigation is concerned with seepage-control canal lining made of geosynthetic materials (GSM): polymer geomembranes and bentonitic mats (bentomats) with protective coatings. Efficiency and longevity criteria of lining made of geomembranes, bentomats and protective coatings (concrete, stone, gabi-on, and soil) have been stated. New lining designs with GSM of high reliability are proposed, including two or three layers of seepage-control lining made of bentomats and geomembranes, as well as protective layers made of geotextiles, rock filling, gabions. We have considered the effectiveness of already constructed sections of Bentofix bentomat linings at Donskoy principal canal (Rostov region, Russia) according to the following three criteria: Filtration costs of the bentomat lining compared to the ground bed, Efficiency degree due to the bentomat lining compared to the alternative options, Filtering resistances of the bentomat lining compared to the alternative options. We have developed a technique to assess the effectiveness of bentonite mats taking into account the regeneration (self-healing) of possible damage due to the regeneration of Ca-bentonite. It is based on the method of successive change of steady states, when the nonsteady process of filtering through damages of the bentomat is divided into a number of steady states. Studies of the aging coefficient of the geomembrane made of polyethylene (HDPE) by the modulus of elongation in the test basin during the period of 8-10 years have made it possible to extrapolate these data and determine the longevity (service life). There is also a calculation of the geomembrane longevity according to the Arrhenius equation. We have made a comparative analysis of the efficiency of various types of canal linings which showed that the most effective type is the bentomat liner, which also has the highest service life.