Beverages produced by kefir are acid, slightly carbonated and alcoholic as a result of lactic and alcoholic fermentations by kefir. They can show prebiotic and/or probiotic properties depending on the grains, substrates and conditions of fermentation. The aim of this study was to evaluate the fermentation of plant extract (“vegetable milks”) [almond (AL), coconut (C), oat (O), rice (R), soybean (S) and soybean supplement with glucose (SG)] by water kefir grains (WK) and compare them to cow milk [whole (WM), lactose-free (LFM) and skimmed (SM)] fermented beverages. The fermentations were conducted by inoculating 5 %w/w of WK, at room temperature, without agitation, for 24 hours. The evaluated responses were cellular growth (X), yield (Y), CO2 production, soluble solids concentration (SS), total solids (TS), pH and acidity (A). The results obtained were: X = 2.3-23.6%, Y = 92.1-95.0%, CO2 = 3.45-7.43%, SSfinal = 3.0 a 13.0 °Brix, pHfinal = 5.66-6.18; Afinal = 0.03-0.47% and TS = 4.37-12.43%. SG, LFM and S were substrates that led to larger X, while SG and LFM led to bigger final A, indicating the efficiency of these substrates to lactic fermentation. SG and C showed a larger CO2 production, indicating greater intensity of the alcoholic fermentation. The use of SG (adding 3% of glucose) and LFM (hydrolyzed lactose) improved the performance of the fermentation, indicating that the presence of monosaccharides had a positive effect on the performance of WK. The extracts of AL, O and R had a poorer performance for X and A, which can be attributed to the smaller initial SS. The C extract had the worst performance, probably due to the small initial SS and high fat content. All used substrates showed potential of application for the production of fermented beverages by WK, although SG (non-dairy) and LFM (dairy) were the most promising.