A systematic study of three well-known bioprotectant sugars - trehalose, sucrose and maltose - in water solutions has been performed at different concentrations and temperatures using molecular-dynamics simulations. A variety of relevant probes such as the size of hydrogen-bonded water clusters, the orientational order parameter q, the Voronoi volume and the dynamical structure factor have been determined to describe the effect of the three disaccharides on water quantitatively. This investigation points out different structural and dynamical behaviours for which a threshold concentration φA and a crossover temperature TA emerge. A "destructuring" effect on the water network and a slowing-down of its dynamics are highlighted. These results suggest narrow links between the different scenarios tentatively explaining bioprotection.